chatgpt and coredns 101

gistfile1.txt

What is coredns
CoreDNS is an open-source Domain Name System (DNS) server software that can be used to provide DNS services for applications and services running in cloud-native environments. It is written in Go and is designed to be highly modular and extensible, allowing users to customize its functionality to suit their specific needs.

CoreDNS is often used as a replacement for traditional DNS servers like BIND, which can be difficult to configure and manage in cloud-native environments. CoreDNS supports a wide range of DNS features, including DNS-over-TLS, DNS-over-HTTPS, DNSSEC, and plugin-based customization of DNS functionality.

CoreDNS is used in many cloud-native platforms, including Kubernetes, which uses CoreDNS as its default DNS server. It can also be used as a standalone DNS server or as a component in larger cloud-native architectures.




Vijaykumar Jain
How to configure coredns for simple domain
Configuring CoreDNS for a simple domain involves creating a Corefile that defines the domain and its associated DNS records. Here is an example of how to configure CoreDNS for a domain "example.com" with a single A record pointing to an IP address "192.0.2.1":

Create a Corefile: The first step is to create a Corefile in a directory accessible to CoreDNS. For example, you can create a file named "Corefile" in the current directory with the following contents:
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example.com {
    file /etc/coredns/example.com.db
}
This Corefile defines a DNS zone for "example.com" and specifies that the zone's DNS records should be read from the file "/etc/coredns/example.com.db".

Create a zone file: The next step is to create a zone file that contains the DNS records for the domain. In this example, we'll create a file named "example.com.db" in the directory "/etc/coredns" with the following contents:
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$ORIGIN example.com.
@    IN    SOA    ns1.example.com. hostmaster.example.com. (
                     2023021801 ; serial
                     1d         ; refresh
                     2h         ; retry
                     4w         ; expire
                     1h         ; minimum
                     )
     IN    NS     ns1.example.com.

ns1   IN    A      192.0.2.1
This file defines the SOA and NS records for the domain and a single A record for the host "ns1" pointing to the IP address "192.0.2.1".

Start CoreDNS: The final step is to start CoreDNS with the Corefile you created. If CoreDNS is installed as a system service, you can start it using the following command:
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sudo systemctl start coredns
Once CoreDNS is running, it should be able to serve DNS requests for the domain "example.com" and return the A record for "ns1.example.com" when queried.




Vijaykumar Jain
How to add a reverse address in coredns 
Adding a reverse address in CoreDNS involves creating a zone file with PTR records that map IP addresses to hostnames, and modifying the Corefile to include the reverse address zone.

Here's an example of how to add a reverse address zone for the IP address range "192.0.2.0/24":

Create a zone file: The first step is to create a zone file that contains the PTR records for the IP addresses in the reverse address zone. In this example, we'll create a file named "2.0.192.in-addr.arpa.db" in the directory "/etc/coredns" with the following contents:
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$ORIGIN 2.0.192.in-addr.arpa.
@    IN    SOA    ns1.example.com. hostmaster.example.com. (
                     2023021801 ; serial
                     1d         ; refresh
                     2h         ; retry
                     4w         ; expire
                     1h         ; minimum
                     )
     IN    NS     ns1.example.com.

1    IN    PTR    ns1.example.com.
This file defines the SOA and NS records for the reverse address zone and a single PTR record for the IP address "192.0.2.1" mapping it to the hostname "ns1.example.com".

Modify the Corefile: The next step is to modify the Corefile to include the reverse address zone. Add the following section to the Corefile:
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2.0.192.in-addr.arpa {
    file /etc/coredns/2.0.192.in-addr.arpa.db
}
This section defines the reverse address zone "2.0.192.in-addr.arpa" and specifies that the zone's DNS records should be read from the file "/etc/coredns/2.0.192.in-addr.arpa.db".

Restart CoreDNS: The final step is to restart CoreDNS to load the new configuration. If CoreDNS is installed as a system service, you can restart it using the following command:
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sudo systemctl restart coredns
Once CoreDNS is running with the new configuration, it should be able to respond to reverse DNS queries for IP addresses in the range "192.0.2.0/24" and return the PTR record for the IP address "192.0.2.1" mapping it to the hostname "ns1.example.com".




Vijaykumar Jain
Can I add the entries using an api or cli
Yes, you can add DNS entries to CoreDNS using its API or CLI.

To add DNS entries using the CoreDNS API, you can use a tool like curl to send a POST request to the CoreDNS server. For example, to add an A record for "www.example.com" with IP address "192.0.2.1", you could send the following request:

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curl -X POST -d '{"dns": {"zones": [{"name": "example.com.", "records": [{"name": "www", "type": "A", "address": "192.0.2.1"}]}]}}' http://localhost:8080/api/v1/up
This request sends a JSON payload to the CoreDNS server's /api/v1/up endpoint, which adds the A record for "www.example.com" to the "example.com" DNS zone.

Alternatively, you can add DNS entries using the CoreDNS CLI. The CoreDNS CLI includes a dns subcommand that can be used to add and manage DNS entries. For example, to add the same A record as above, you could use the following command:

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coredns -conf /etc/coredns/Corefile dns add example.com www A 192.0.2.1
This command adds an A record for "www.example.com" with IP address "192.0.2.1" to the "example.com" DNS zone using the Corefile configuration at /etc/coredns/Corefile.

Both the API and CLI methods allow you to add DNS entries dynamically to CoreDNS without having to manually edit zone files or restart the CoreDNS server.




Vijaykumar Jain
How to add a ptr record using api and cli
To add a PTR record using the CoreDNS API, you can use a tool like curl to send a POST request to the CoreDNS server. For example, to add a PTR record for the IP address "192.0.2.1" mapping it to the hostname "www.example.com.", you could send the following request:

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curl -X POST -d '{"dns": {"zones": [{"name": "2.0.192.in-addr.arpa.", "records": [{"name": "1", "type": "PTR", "ptrdname": "www.example.com."}]}]}}' http://localhost:8080/api/v1/up
This request sends a JSON payload to the CoreDNS server's /api/v1/up endpoint, which adds the PTR record for the IP address "192.0.2.1" to the "2.0.192.in-addr.arpa" reverse DNS zone.

Alternatively, you can add a PTR record using the CoreDNS CLI. The CoreDNS CLI includes a dns subcommand that can be used to add and manage DNS entries. For example, to add the same PTR record as above, you could use the following command:

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coredns -conf /etc/coredns/Corefile dns add 2.0.192.in-addr.arpa 1 PTR www.example.com.
This command adds a PTR record for the IP address "192.0.2.1" mapping it to the hostname "www.example.com." in the "2.0.192.in-addr.arpa" reverse DNS zone using the Corefile configuration at /etc/coredns/Corefile.

Both the API and CLI methods allow you to add PTR records dynamically to CoreDNS without having to manually edit zone files or restart the CoreDNS server.




Vijaykumar Jain
Can we chain multiple coredns servers to look up hierarchically 
Yes, you can chain multiple CoreDNS servers to perform hierarchical DNS lookups. This is known as DNS forwarding or DNS chaining.

To set up DNS forwarding with CoreDNS, you need to configure one CoreDNS server to forward requests to another CoreDNS server. This can be done by adding a forward plugin block to the Corefile configuration of the first CoreDNS server.

For example, if you have two CoreDNS servers with IP addresses "192.168.1.10" and "192.168.1.20", you can configure the first server to forward requests to the second server by adding the following forward plugin block to its Corefile:

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forward . 192.168.1.20
This configuration tells CoreDNS to forward all DNS queries for zones it does not manage (denoted by the . wildcard) to the CoreDNS server at IP address "192.168.1.20".

You can chain more than two CoreDNS servers by adding additional forward plugin blocks to the Corefile of each server in the chain. For example, if you have a third CoreDNS server at IP address "192.168.1.30", you can configure the second server to forward requests to the third server by adding the following forward plugin block to its Corefile:

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forward . 192.168.1.30
This configuration tells the second CoreDNS server to forward all DNS queries for zones it does not manage to the CoreDNS server at IP address "192.168.1.30".

By chaining multiple CoreDNS servers in this way, you can create a hierarchy of DNS servers that can be used to resolve DNS queries for a large number of domains.




Vijaykumar Jain
How to make coredns servers highly available 
To make CoreDNS servers highly available, you can set up a cluster of multiple CoreDNS servers and configure them to work together to provide DNS resolution services. There are several approaches to achieving this, depending on the requirements of your environment.

One approach is to use a load balancer to distribute incoming DNS requests across multiple CoreDNS servers in the cluster. This can be done by setting up a load balancer in front of the CoreDNS servers and configuring it to balance traffic based on various algorithms such as round-robin, least connections, or IP hash. By doing so, you can ensure that incoming DNS requests are evenly distributed across the CoreDNS servers in the cluster, providing a higher level of availability.

Another approach is to use a distributed DNS architecture, such as DNS Anycast, to provide high availability. In this approach, multiple CoreDNS servers are configured with the same IP address, and network routing is used to direct incoming DNS requests to the closest CoreDNS server based on network topology. This can help reduce latency and provide faster DNS resolution times, while also providing redundancy and failover in case one CoreDNS server in the cluster goes down.

In addition, you can configure CoreDNS to use a backend storage system for storing DNS records, such as a distributed key-value store or a database, to ensure that DNS records are replicated and available across multiple servers in the cluster. This can help ensure that DNS resolution services are not affected if one CoreDNS server fails or becomes unavailable.

Finally, you can set up monitoring and alerting systems to detect and respond to issues that may arise in the CoreDNS cluster, such as server failures, network issues, or DNS misconfigurations. By having a robust monitoring and alerting system in place, you can proactively identify and resolve issues before they affect DNS resolution services for your users.




Vijaykumar Jain
How to create a cluster of corednd servers with replicated data 
To create a cluster of CoreDNS servers with replicated data, you can use a distributed key-value store as a backend for storing DNS records. This allows you to store DNS records in a centralized location that can be accessed by all CoreDNS servers in the cluster, ensuring that all servers have the same copy of the DNS records.

One popular key-value store for this purpose is etcd, which is a distributed, consistent key-value store that is often used in Kubernetes environments. Here's how you can set up a cluster of CoreDNS servers with replicated data using etcd:

Set up an etcd cluster: First, set up an etcd cluster that will be used to store DNS records. You can follow the instructions in the etcd documentation to set up a cluster.

Configure CoreDNS to use etcd as a backend: Next, configure CoreDNS to use etcd as a backend for storing DNS records. To do this, add an etcd plugin block to the Corefile configuration of each CoreDNS server in the cluster, specifying the etcd endpoint and credentials:

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etcd {
    endpoints http://etcd1:2379,http://etcd2:2379,http://etcd3:2379
    tls off
    path /dns
    upstream /etc/resolv.conf
}
This configuration tells CoreDNS to use the etcd cluster at the specified endpoints for storing DNS records, with TLS disabled and a path of /dns for the DNS zone. The upstream option specifies the location of the system DNS resolver, which can be used to forward requests to upstream DNS servers if the requested domain is not found in etcd.

Start the CoreDNS servers: Start up each CoreDNS server in the cluster with the updated Corefile configuration. You can use a container orchestration platform such as Kubernetes to manage the CoreDNS servers, or start them manually on individual hosts.

With this setup, all CoreDNS servers in the cluster will be able to read and write DNS records to the etcd key-value store, ensuring that all servers have the same copy of the DNS records. This provides a highly available and fault-tolerant DNS resolution service, with automatic failover and replication of DNS records across the cluster.




Vijaykumar Jain
Are there health checks to identify slow node or too busy node.
Yes, CoreDNS supports health checks that can be used to identify slow or too busy nodes in a cluster. These health checks can be used to monitor the status of each CoreDNS server in the cluster and ensure that DNS resolution services are available and responsive.

One approach to implementing health checks is to use a monitoring tool such as Prometheus, which is a popular open-source monitoring and alerting system. Prometheus can be used to scrape metrics from each CoreDNS server in the cluster and provide insights into the performance and health of the servers.

To enable Prometheus monitoring, you can add a prometheus plugin block to the Corefile configuration of each CoreDNS server in the cluster:

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prometheus
This configuration tells CoreDNS to expose metrics in the Prometheus format on the default port of 9153. You can then configure Prometheus to scrape metrics from each CoreDNS server and visualize the data in a dashboard.

In addition to monitoring server performance, you can also use health checks to monitor the availability and responsiveness of DNS resolution services. CoreDNS supports a health plugin that can be used to check the health of each server in the cluster based on a configurable endpoint. For example, you can configure each CoreDNS server to expose a /health endpoint that returns a 200 status code if the server is healthy, and a 500 status code if the server is unhealthy or overloaded.

To enable the health plugin, you can add a health plugin block to the Corefile configuration of each CoreDNS server:

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health
This configuration tells CoreDNS to expose a health endpoint on the default path of /health that returns a 200 status code if the server is healthy.

By using these health checks, you can monitor the performance and availability of each CoreDNS server in the cluster, and quickly identify and respond to issues such as slow or overloaded nodes.




Vijaykumar Jain
Is it advisable to have coredns servers across the Wan 
Having CoreDNS servers across a WAN (Wide Area Network) can be done, but it's not always advisable, depending on the specific circumstances of the deployment.

Here are a few factors to consider when deciding whether to deploy CoreDNS servers across a WAN:

Latency: WAN connections typically have higher latency than local connections, which can slow down DNS resolution times. If the WAN latency is significant, it may be better to deploy separate DNS servers for each location.

Bandwidth: DNS traffic is generally lightweight and does not consume a lot of bandwidth. However, if you have a large number of clients at each location or are using DNS-based load balancing, the bandwidth requirements may increase.

Network reliability: WAN connections can be less reliable than local connections, which can result in intermittent DNS resolution issues. You may need to implement redundancy measures such as load balancing or failover mechanisms to ensure that DNS resolution services remain available.

Security: If you are using CoreDNS servers across a WAN, you need to ensure that the communication between the servers and clients is secure. This can be done using encryption and authentication mechanisms such as TLS.

In general, if the WAN connections are stable, reliable, and have low latency, it may be possible to deploy CoreDNS servers across a WAN. However, if the WAN connections are not ideal, it may be better to deploy separate DNS servers for each location and configure them to communicate with each other as needed.

Ultimately, the decision to deploy CoreDNS servers across a WAN depends on the specific requirements and constraints of your deployment. It's important to evaluate the network conditions, bandwidth, and security requirements before deciding whether to use CoreDNS servers across a WAN.




Vijaykumar Jain
Coredns has multiple moving parts, to upgrade coredns or etcd can result in a downtime. Or is there another option for online upgrade 
Yes, upgrading CoreDNS or etcd can result in downtime, especially if you need to upgrade multiple components of the system. However, there are several strategies you can use to minimize or eliminate downtime during upgrades.

Here are a few strategies to consider:

Rolling upgrades: Instead of upgrading all the components at once, you can perform rolling upgrades, upgrading one or a few components at a time. This approach ensures that there is always a functioning DNS server in the cluster, even if some of the components are being upgraded.

Blue-green deployments: A blue-green deployment involves creating two separate environments, one running the current version of CoreDNS and etcd, and the other running the new version. Clients are gradually switched from the old environment to the new environment, eliminating downtime during the upgrade process.

Canary deployments: A canary deployment involves deploying the new version of CoreDNS or etcd to a small subset of users or nodes first, and then gradually rolling out the upgrade to the rest of the system. This approach allows you to test the new version in a controlled environment before deploying it to the entire system.

High availability: Ensuring that your CoreDNS cluster has high availability can minimize downtime during upgrades. This can be achieved by deploying redundant nodes or using load balancing to distribute traffic across multiple nodes.

Automated testing: Automated testing can help you identify issues with the new version of CoreDNS or etcd before deploying it to the production environment. This can reduce the risk of downtime and ensure that the upgraded system works as expected.

In summary, there are several strategies you can use to upgrade CoreDNS or etcd without causing downtime. Rolling upgrades, blue-green deployments, canary deployments, high availability, and automated testing are all viable options that can help minimize the risk of downtime during upgrades.




Vijaykumar Jain
Can etcd replicate from lower version to higher version 
In general, it is possible to replicate data from a lower version of etcd to a higher version, but it's important to note that there may be compatibility issues that can affect the replication process.

Here are a few factors to consider when replicating data from a lower version of etcd to a higher version:

Compatibility: Different versions of etcd may have different data formats, APIs, and configuration options. It's important to check the release notes and documentation for the specific versions of etcd you're using to ensure compatibility.

Upgrade path: It's generally recommended to upgrade etcd one version at a time, rather than skipping versions. This ensures that any compatibility issues or other problems are addressed before moving to the next version.

Backup and restore: Before upgrading etcd, it's important to back up the data to ensure that you can restore it in case of any issues. You may also want to test the restore process to ensure that it works as expected.

Testing: After upgrading etcd, it's important to test the system thoroughly to ensure that the data is being replicated correctly and that there are no issues with the new version.

In summary, it is possible to replicate data from a lower version of etcd to a higher version, but it's important to ensure compatibility, follow the recommended upgrade path, backup and restore the data, and test the system thoroughly after upgrading.




Vijaykumar Jain
Does coredns server cache entries, how to configure ttl and srv records 
Yes, CoreDNS can cache DNS responses to improve performance and reduce the load on upstream servers. By default, CoreDNS caches responses for 5 minutes, but this can be adjusted using the cache plugin.

Here's an example configuration for the cache plugin that sets the cache TTL to 1 hour:

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. {
    cache 1h
    forward . 8.8.8.8
}
In this example, the cache plugin is set to cache responses for 1 hour (1h). The forward plugin is also configured to forward requests to the Google Public DNS resolver at 8.8.8.8.

To configure SRV records in CoreDNS, you can use the srv plugin. Here's an example configuration:

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example.com {
    srv 10 100 80 example1.com
    srv 20 100 80 example2.com
}
In this example, two SRV records are defined for the example.com domain. The first record has a priority of 10, weight of 100, port of 80, and target of example1.com. The second record has a priority of 20, weight of 100, port of 80, and target of example2.com.

You can also set the TTL for SRV records using the ttl option, like this:

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example.com {
    srv 10 100 80 example1.com {
        ttl 3600
    }
    srv 20 100 80 example2.com {
        ttl 3600
    }
}
In this example, the TTL for both SRV records is set to 1 hour (3600 seconds).




Vijaykumar Jain
How to force flush stale dns records before ttl period
CoreDNS caches DNS records according to the time-to-live (TTL) value specified in the response from the authoritative DNS server. However, sometimes you may need to force the cache to be flushed before the TTL period expires, for example, if a record has changed and you need to update the cache immediately.

Here are a few ways to force CoreDNS to flush the cache:

Use the reload command: You can send a SIGHUP signal to the CoreDNS process, which will cause it to reload its configuration and flush the cache. For example, if CoreDNS is running as a systemd service, you can run the following command to reload the configuration and flush the cache:

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systemctl reload coredns
Use the SIGUSR1 signal: You can send a SIGUSR1 signal to the CoreDNS process, which will cause it to flush the cache. For example, you can run the following command to send the SIGUSR1 signal to the CoreDNS process:

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killall -SIGUSR1 coredns
Use the dns plugin: CoreDNS includes a dns plugin that can be used to query the cache and force records to be flushed. Here's an example configuration that uses the dns plugin to flush the cache for the example.com domain:

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example.com {
    dns {
        ttl 0
    }
    forward . 8.8.8.8
}
In this example, the dns plugin is configured with a TTL of 0, which means that records will be flushed immediately. The forward plugin is also configured to forward requests to the Google Public DNS resolver at 8.8.8.8.

Keep in mind that forcing the cache to be flushed can increase the load on upstream DNS servers and may cause temporary service disruptions. Therefore, it's generally recommended to use this approach only when necessary, and to ensure that the cache TTL values are appropriate for your use case.




Vijaykumar Jain
In case of microservices, there can be stale entries returned by some coredns servers if a new service srv record is created but all the old srv records pointing to ip port are not deleted. Is there a way to ensure app only queries the last updated coredns server 
In a distributed microservices environment where multiple CoreDNS servers are serving DNS queries, it's possible for stale entries to be returned by some servers if new SRV records are created but the old ones are not deleted. One way to ensure that your application only queries the most up-to-date CoreDNS server is to use a DNS resolver that supports health checking and load balancing.

For example, you can use a resolver like Consul or Kubernetes DNS, which can perform health checks on SRV records and route traffic to healthy instances. These resolvers also support load balancing and can distribute traffic evenly across multiple instances.

With Consul, for example, you can configure health checks on SRV records using the check parameter in the SRV record definition. Here's an example:

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my-service.service.consul.  IN  SRV  1  1  80  web1.node.dc1.consul.,check=http://web1.node.dc1.consul/health
In this example, a health check is configured on the SRV record using the check parameter, which specifies the URL of a health check endpoint. Consul will periodically perform a GET request to this URL, and if the response code is not 200, the instance will be marked as unhealthy and traffic will be routed to other instances.

Similarly, with Kubernetes DNS, you can use the ExternalName service type to create a DNS alias that points to the current healthy SRV record. When a new SRV record is created, the ExternalName service can be updated to point to the new record, effectively ensuring that your application always queries the most up-to-date CoreDNS server.

In summary, using a DNS resolver that supports health checking and load balancing can help ensure that your application always queries the most up-to-date CoreDNS server and avoids stale entries.




Vijaykumar Jain
Does coredns allow load balancing, or black holing requests. 
Yes, CoreDNS allows load balancing and black holing of DNS requests.

CoreDNS supports a variety of load balancing algorithms, including round-robin, least connection, and IP hash. To configure load balancing, you can use the loadbalance plugin, which is enabled by default. You can also configure the specific load balancing algorithm and other options using the lb directive.

For example, here's how you can configure round-robin load balancing for a set of A records:

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example.com {
    ttl 3600
    A 192.0.2.1
    A 192.0.2.2
    loadbalance round_robin
}
In this example, the loadbalance plugin is used to distribute queries to the two A records in a round-robin fashion.

CoreDNS also supports black holing of DNS requests, which involves dropping or rejecting requests for certain domains or IP addresses. This can be useful for blocking malicious traffic or preventing DNS amplification attacks.

To configure black holing, you can use the block plugin, which allows you to specify the domains or IP addresses to block. For example, here's how you can block all queries for the example.com domain:

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example.com {
    block
}
In this example, all queries for the example.com domain will be dropped without a response. You can also configure more specific blocking rules using regular expressions or IP address ranges.

In summary, CoreDNS provides a variety of plugins for load balancing and black holing DNS requests, allowing you to customize the behavior of your DNS server to suit your needs.




Vijaykumar Jain
Is coredns single threaded or multi threaded, can it run on multiple cpu
CoreDNS is a multi-threaded DNS server that can take advantage of multiple CPUs.

When CoreDNS starts up, it creates a pool of worker threads to handle incoming DNS queries. Each worker thread is responsible for handling a subset of queries, and can run in parallel with other threads on separate CPU cores. By default, CoreDNS creates one worker thread for each available CPU core, up to a maximum of 8 threads.

The number of worker threads can be adjusted using the -t command-line option or the threads configuration directive. For example, to configure CoreDNS to use 16 worker threads, you can use the following configuration:

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. {
    # other plugins
    threads 16
}
In addition to worker threads, CoreDNS also uses a single management thread to handle configuration updates and other administrative tasks.

Overall, CoreDNS is designed to be scalable and performant, and can take advantage of multiple CPUs to handle a high volume of DNS queries.




Vijaykumar Jain
How to split up one zone into multiple sub zones like prod, preproduction, ci to ensure we can restrict connection from ci to prod
To split up a single zone into multiple subzones, you can create separate zone files for each subzone and configure CoreDNS to serve each zone separately.

Here's an example configuration that splits up the example.com zone into three subzones: prod.example.com, preprod.example.com, and ci.example.com. Each subzone is served by a separate file, which can be stored in a different directory if desired.

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# /etc/coredns/Corefile

# Serve the prod.example.com zone
prod.example.com {
    file /etc/coredns/prod.example.com.db
}

# Serve the preprod.example.com zone
preprod.example.com {
    file /etc/coredns/preprod.example.com.db
}

# Serve the ci.example.com zone
ci.example.com {
    file /etc/coredns/ci.example.com.db
}
In this example, each subzone is configured to use a separate zone file using the file plugin. You'll need to create a separate zone file for each subzone, which should contain the relevant DNS records for that subzone.

To restrict connections between subzones, you can use network-based access controls or firewall rules to block traffic between the relevant IP addresses or subnets. For example, you might configure firewall rules to allow traffic between the ci.example.com subnet and the preprod.example.com subnet, but block traffic to the prod.example.com subnet.

Overall, splitting a single zone into multiple subzones can help improve security by restricting access between different environments or stages of development.




Vijaykumar Jain
can we use coredns and bind9 together
Yes, you can use CoreDNS and BIND9 together in the same DNS infrastructure, although it can be somewhat complicated to set up and manage.

One common scenario where you might use both CoreDNS and BIND9 is in a mixed environment that includes both traditional DNS servers and containerized applications. For example, you might use BIND9 to serve the DNS needs of your traditional infrastructure, while using CoreDNS to provide DNS services for containerized applications running on Kubernetes.

To use CoreDNS and BIND9 together, you'll need to configure them to avoid conflicts and ensure that DNS queries are routed to the correct server for the relevant zone.

Here are a few key considerations when using CoreDNS and BIND9 together:

Avoid overlapping zones: Make sure that each DNS server is responsible for serving a non-overlapping set of zones to avoid conflicts. You can achieve this by carefully planning your zone hierarchy and delegating subdomains to the appropriate server.

Use different port numbers: By default, both CoreDNS and BIND9 listen on port 53, which can cause conflicts. To avoid this, you can configure one of the servers to listen on a different port, such as 5353 or 1053.

Configure forwarding: If you have overlapping zones or need to route DNS queries between servers, you can use DNS forwarding to route queries from one server to another. For example, you might configure CoreDNS to forward queries for a particular zone to your BIND9 server, or vice versa.

Consider DNSSEC: If you're using DNSSEC to sign your zones, you'll need to make sure that both servers are configured to use the same keys and algorithms to ensure that DNSSEC validation works correctly.

Overall, using CoreDNS and BIND9 together can be a bit tricky, but it's possible to set up a working configuration with careful planning and configuration.




Vijaykumar Jain
how to sign zones using dnssec in coredns
To sign zones using DNSSEC in CoreDNS, you'll need to perform the following steps:

Generate DNSSEC keys: First, you'll need to generate the DNSSEC keys that will be used to sign your zones. You can use a tool like dnssec-keygen to generate the necessary keys.

Configure CoreDNS to sign zones: Once you have your DNSSEC keys, you'll need to configure CoreDNS to sign your zones using those keys. This involves adding a dnssec plugin block to your CoreDNS configuration file, which specifies the keys and algorithms to use for signing. Here's an example dnssec plugin block:

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dnssec {
    key-file /etc/coredns/keys/Kexample.com.+008+12345.key
    signed-zones example.com {
        key-directory /etc/coredns/keys/
        active-signing
    }
}
In this example, we're telling CoreDNS to sign the example.com zone using the key located at /etc/coredns/keys/Kexample.com.+008+12345.key.

Configure your registrar: In order for DNSSEC to work correctly, you'll need to configure your domain registrar to include the DNSSEC key information in the DNS records for your domain. This typically involves adding DS records to your domain's zone file.

Verify DNSSEC operation: Once you've configured DNSSEC for your domain, you should verify that it's working correctly using a tool like dig or dnssec-verify.

Note that DNSSEC can be complex to set up and manage, and it's important to follow best practices to ensure the security and integrity of your DNS infrastructure. In particular, you'll need to carefully manage your DNSSEC keys to prevent them from being compromised, and you'll need to regularly monitor your DNSSEC configuration for signs of tampering or errors.




Vijaykumar Jain
will i need a key to lookup records when i make use of dnssec
No, you will not need a key to look up records when using DNSSEC. The purpose of DNSSEC is to provide a mechanism for verifying the authenticity of DNS responses, not to restrict access to DNS data.

When DNSSEC is used, each DNS response is digitally signed by the server that provides the response, using a private key that is associated with the domain being queried. The client can then use the corresponding public key, which is published in the domain's DNS records as a DNSKEY record, to verify the signature and ensure that the response has not been tampered with.

However, the process of verifying DNSSEC signatures is typically handled automatically by the client's DNS resolver (such as the resolver provided by your ISP or your organization's network), and does not require any manual intervention or use of keys by the end user.

So in short, you will not need a key to look up records when using DNSSEC, but DNSSEC can provide additional security and integrity checks to ensure that the DNS responses you receive are authentic and have not been tampered with.




Vijaykumar Jain
what other useful plugins are available with coredns
CoreDNS has a wide range of plugins that can be used to extend its functionality and customize its behavior. Some of the useful plugins available with CoreDNS include:

Forward - Allows forwarding of DNS requests to upstream servers.
Cache - Caches DNS responses to improve performance and reduce network traffic.
AutoReload - Automatically reloads CoreDNS configuration when changes are detected.
Debug - Logs debugging information to help diagnose issues.
Prometheus - Exposes metrics about CoreDNS performance and usage for monitoring purposes.
Health - Allows monitoring of CoreDNS health and availability status.
Rewrite - Rewrites DNS requests and responses to modify their behavior.
Kubernetes - Integrates with Kubernetes to provide DNS-based service discovery and load balancing.
DNSSEC - Enables DNSSEC validation and signing of DNS responses for improved security.
Route53 - Integrates with Amazon Route 53 to provide DNS-based service discovery and load balancing on AWS.
These plugins can be combined and configured in various ways to create custom DNS servers tailored to specific use cases and environments.




Vijaykumar Jain
i need to drain one coredns server for maintenance without dropping requests , how to ensure no requests are dropped and the node can be taken out
To drain a CoreDNS server for maintenance without dropping requests, you can use a technique called "graceful shutdown". This involves gradually reducing the traffic to the server over a period of time, allowing existing connections to be completed while preventing new connections from being established.

Here are the steps to perform a graceful shutdown of a CoreDNS server:

Reduce the traffic to the server by updating the DNS records to point to the other servers in the cluster. This can be done by adjusting the DNS load balancer settings or by updating the DNS records directly.
Set the CoreDNS server's replica count to zero, so that Kubernetes stops sending new requests to the server. You can do this using the kubectl scale command, for example: kubectl scale --replicas=0 deployment/coredns.
Wait for the existing connections to be completed. You can monitor the number of active connections using tools like netstat, ss, or Kubernetes metrics. This step can take several minutes or longer, depending on the current traffic load.
Once all the connections have been completed, you can safely shut down the CoreDNS server for maintenance.
To bring the server back into the cluster, you can reverse the above steps: update the DNS records or load balancer settings to include the server, set the replica count to its original value using kubectl scale, and monitor the server to ensure it is handling requests normally.




Vijaykumar Jain
but i am not using kubernetes in my setup. simple coredns servers
If you are not using Kubernetes, the steps to perform a graceful shutdown of a CoreDNS server can vary depending on your specific setup. However, the general idea of gradually reducing the traffic to the server and allowing existing connections to be completed still applies.

Here are some general steps you can follow to gracefully drain a CoreDNS server without dropping requests:

Reduce the traffic to the server by updating the DNS records to point to the other servers in the cluster. This can be done by adjusting the DNS load balancer settings or by updating the DNS records directly.
Monitor the server's traffic and connections to ensure that the number of active connections gradually decreases over time. You can use tools like netstat, ss, or DNS query logs to monitor the traffic.
Once the number of active connections has decreased to a minimum, you can safely shut down the CoreDNS server for maintenance.
After the maintenance is complete, bring the server back online and update the DNS records to include the server again.
It's important to note that the specific steps and techniques used to gracefully drain a CoreDNS server may depend on your specific setup, including factors like the number of servers in the cluster, the traffic load, and the types of requests being handled.




Vijaykumar Jain
how to find out dangling entries of A record or PTR records. For example, i have several dead entries in zone files which are not in use, but they done have PTR records. how to ensure A records and reverse PTR records are in sync and there are no dangling PTR records
To find out dangling entries of A record or PTR records, you can use various tools and techniques, depending on your setup and environment. Here are a few methods that you can use:

DNS query logs: You can enable DNS query logging in your CoreDNS configuration to log all the DNS queries that are received by the server. You can then analyze these logs to identify any A or PTR record queries that are not being answered by the server. These queries may indicate dangling entries in your zone files that need to be cleaned up.

Zone file analysis: You can manually review the zone files for your domain to identify any A or PTR records that are not being used or are no longer valid. You can also use tools like named-checkzone (for BIND) or coredns -validate (for CoreDNS) to check the syntax and validity of your zone files.

Reverse lookup zone analysis: You can also review your reverse lookup zone files to ensure that they are in sync with your forward lookup zone files. For example, you can use the dig -x command to perform reverse lookup queries for your A records and ensure that the corresponding PTR records are correctly configured.

Third-party tools: There are also various third-party tools available that can help you identify dangling DNS entries, including tools like DNSViz, Zonemaster, and DNSSEC-Analyzer.

By using one or more of these methods, you can identify any dangling A or PTR records in your zone files and take the necessary steps to clean up and ensure that your A records and reverse PTR records are in sync.




Vijaykumar Jain
but making so many dns queries can create a burst of network storm. is it possible to query etcd directly 
Yes, you can query etcd directly instead of relying on CoreDNS to retrieve DNS records. Etcd provides a HTTP API that you can use to query the data stored in the etcd cluster. You can use tools like curl or programming languages like Python to make HTTP requests to the etcd API and retrieve the DNS records you need.

Here's an example of how you can use curl to query etcd for DNS records:

graphql
Copy code
$ curl http://<etcd-host>:<etcd-port>/v3alpha/kv/range -X POST -d '{"key": "<dns-zone>", "range_end": "<dns-zone>\uffff", "sort_order": "ASCEND", "sort_target": "KEY", "serializable": false}'
In this example, you'll need to replace <etcd-host> and <etcd-port> with the IP address and port of your etcd cluster, and <dns-zone> with the name of the DNS zone you want to query.

This command will return a JSON-encoded response containing all the DNS records stored in the specified zone. You can then parse this response and extract the records you need.

However, keep in mind that querying etcd directly can be more complex and error-prone than using CoreDNS, especially if you have a complex DNS setup with multiple zones and records. Additionally, querying etcd directly bypasses any caching or load balancing features provided by CoreDNS, so you may need to implement these features yourself if you choose to query etcd directly.