Working HA Proxy config example with a fallback backend

README.md

Simple HA proxy with fallback backend

To run:

docker compose up # or docker-compose up if not using the docker plugin

In another terminal the run the following:

curl -v -d '{"key1":"value1", "key2":"value2"}' -H "Content-Type: application/json" -X POST  localhost:4080/test

You will then see in that the container called main-backend-1 handles the request, something like:

ha-proxy-failover-main-backend-1    | 172.27.0.4 - - [20/Mar/2023:15:11:23 +0000] "POST /test HTTP/1.1" 200 0 "-" "curl/7.81.0" "-"

To simulate the main backend going down just run:

docker compose stop main-backend

Then the next time you make a curl request it will block and might also timeout. Eventually HA proxy (after about 5 seconds or so) will register the main backend as down and route all requests to the backup backend. In the logs you will then see the request being handled by ``. You might need to make the curl request again.

ha-proxy-failover-main-backend-1 exited with code 0
ha-proxy-failover-proxy-1           | [WARNING]  (7) : Server bk_main/s1 is DOWN, reason: Layer4 timeout, check duration: 2001ms. 0 active and 0 backup servers left. 1 sessions active, 0 requeued, 0 remaining in queue.
ha-proxy-failover-proxy-1           | [ALERT]    (7) : backend 'bk_main' has no server available!
ha-proxy-failover-backup-backend-1  | 172.27.0.4 - - [20/Mar/2023:15:17:42 +0000] "POST /test HTTP/1.1" 200 0 "-" "curl/7.81.0" "-"

The HA config can be improved to not use a network check and instead an actual health check. So it could look like something like:

backend bk_main
    mode http
    option httpchk
    http-check send meth GET  uri /health
    http-request set-header X-MY-HEADER "some_value/bk_main"
    server s1 main-backend:80 check

docker-compose.yaml

---
version: "3.9"
services:
  proxy:
    image: haproxy:2.6
    ports:
      # curl -v -d '{"key1":"value1", "key2":"value2"}' -H "Content-Type: application/json" -X POST  localhost:4080/test
      - "4080:80"
    volumes:
      - type: bind
        source: failover_ha.cfg
        target: /usr/local/etc/haproxy/haproxy.cfg

  main-backend:
    image: nginx:stable
    ports:
      # curl -v -d '{"key1":"value1", "key2":"value2"}' -H "Content-Type: application/json" -X POST  localhost:4081/test
      - "4081:80"
    volumes:
      - type: bind
        source: nginx_always_200.conf
        target: /etc/nginx/conf.d/default.conf
        read_only: true

  backup-backend:
    image: nginx:stable
    ports:
      # curl -v -d '{"key1":"value1", "key2":"value2"}' -H "Content-Type: application/json" -X POST  localhost:4082/test
      - "4082:80"
    volumes:
      - type: bind
        source: nginx_always_200.conf
        target: /etc/nginx/conf.d/default.conf
        read_only: true

failover_ha.cfg

# Basic configuration
global
    log 127.0.0.1 local0
    maxconn 4096
    stats socket /tmp/haproxy

# Some sane defaults
defaults
    mode    http
    log     global
    option  dontlognull
    retries 3
    timeout client 5s
    timeout server 5s
    timeout connect 5s

# This declares a view into HAProxy statistics, on port 3833
# You do not need credentials to view this page and you can
# turn it off once you are done with setup.
listen stats
    bind *:3833
    mode http
    stats enable
    stats uri /

# This section is to reload DNS Records
# Replace <DNS_SERVER_IP> and <DNS_SECONDARY_SERVER_IP> with your DNS Server IP addresses.
# For HAProxy 1.8 and newer
resolvers my-dns
    nameserver dns1 1.1.1.1:53
    nameserver dns2 8.8.8.8:53
    resolve_retries 3
    timeout resolve 2s
    timeout retry 1s
    accepted_payload_size 8192
    hold valid 10s
    hold obsolete 60s

# This the entrypoint
frontend http-in
    bind *:80
    
    # detect capacity issues in production farm
    acl MAIN_not_enough_capacity nbsrv(bk_main) le 0
    # failover traffic to backup farm
    use_backend bk_main_backup if MAIN_not_enough_capacity

    default_backend bk_main

# This is the primary backend
backend bk_main
    mode http
    http-request set-header X-MY-HEADER "some_value/bk_main"
    server s1 main-backend:80 check

backend bk_main_backup
    mode http
    option httpchk
    # Run a HTTP health check on the backend 
    http-check send meth GET  uri /health 
    # Expect a status of 200
    http-check expect status 200
    http-request set-header X-MY-HEADER "some_value/bk_main_backup"
    # Run the check every 10 seconds
    server s1 backup-backend:80 check inter 10s

nginx_always_200.conf

server {
    listen       80;
    listen  [::]:80;
    server_name  localhost;

    location / {
        return 200;
    }    
}