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Ansible setup, config, and ad hoc deep dive
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ansible-setup-ad-hoc-deep-dive.md

Ansible setup, configure, and ad hoc commands deep dive

Ansible is an automation engine that allows for agentless system config and deployment. Ansible operates over SSH and runs Ansible modules on remote systems to complete tasks.

TOC

Ansible setup

Installing ansible

sudo yum install epel-release
sudo yum update && sudo yum install ansible

# Add devices you'll access to /etc/ansible/hosts
sudo vim /etc/ansible/hosts

# Best practice is to create an ansible user in every host in
# the environment so you can authenticate with the same user
# from src to destination.

# CentOs
sudo useradd ansible && sudo passwd ansible
su - ansible

# Ubuntu (prompts for pw)
adduser ansible
su - ansible

# The command below tests connectivity with the ping module (-m)
# and prompts for password (-k)

ansible localhost -m ping -k
localhost | SUCCESS => {
    "changed": false,
    "ping": "pong"
}

Configuring SSH and sudo for ansible

  • Goal is to have a single common user across all hosts.

It's strongly recommended that you set up login via SSH keys so you don't have to type passwords.

    ssh-keygen
    ssh-copy-id centos2.jm

Give ansible sudo access

sudo visudo

# Once in the file, search for "without a password"
# And add the ansible line below the wheel line

# Same thing without a password
# %wheel        ALL=(ALL)       NOPASSWD: ALL
ansible         ALL=(ALL)       NOPASSWD: ALL

Back to table of contents

Ansible configuration

The ansible configuration file

  • sudo vim /etc/ansible/ansible.cfg
  • There's a section called "some basic default values," which you won't likely change starting out.
  • The ansible-config command takes some arguments that allow you to display the running config, all configs, etc. Check out man ansible-config. This utility is avaiable as of ansible 2.4
  • The config properties may be overridden using local files. The first configuration file is used and other files are ignored. Order:
    • ANSIBLE_CONFIG env variable if set
    • ansible.cfg in working directory
    • ~/ansible.cfg
    • /etc/ansible/ansible.cfg

Setting up the ansible inventory

  • The inventory is a list of hosts that ansible manages.

  • The default location is /etc/ansible/hosts

    • You can specify the inventory via ansible -i $file_name
      E.g., ansible -i inventory localhost -m ping
    • You can also set the inventory in ansible.cfg

  • The default file has a lot of examples of what you can do.

    • You can create groups of hosts and specify hosts by name or IP address.

    • You can use a pattern such as www[01:06].example.com for ansible to expand out

        # Example groups

  [ny]
  ny-rt1.example.com
  ny-rt2.example.com
  ny-sw1.example.com
  ny-sw2.example.com

  [routers]
  ny-rt1.example.com
  ny-rt2.example.com

  • You can then execute the command by referencing a host or a group: ansible routers -m ping

Back to table of contents

Understanding ansible ad hoc

The ansible command

  • Ansible ad hoc commands are comparable to bash commands.
  • Playbooks are comparable to bash scripts
  • Syntax for ad hoc command: ansible [-i $inventory] $host [-b] -m $module -a $arg1 [$arg2...] -f $num_forks
    • -b = become, which by default becomes root
    • Example to install software: ansible centos2.jm -b -m yum -a "name=elinks state=installed"
    • Example to remove software: ansible centos2.jm -b -m yum -a "name=elinks state=absent"

Understanding ansible modules

  • Modules are discrete units of code that can be used from the CLI or in a playbook task.
  • Most modules take key=value arguments delimited by whitespace (there are exceptions).
  • Example modules include: ping, setup, yum, service, and copy
  • You can visitdocs.ansible.com and use ctrl + F to search for keywords such as "Cisco IOS."
  • You can also use the ansible-doc command. E.g., ansible-doc ping

The shell and command modules

  • The shell and command modules allow you to run raw commands on a target host.
  • The command module is the default with ansible ad-hoc when no module is specified. It's best practice to use this module unless you require shell features.
  • The shell command is almost identical, except the commands are run in a shell environment.
  • The shell module might be preferred for input/output redirection, env variables, and other shell features not supported by the command module.
  • It's best to use modules that do what you need so you don't need to define success criteria for raw commands.
  • The script module allows you to run entire shell scripts rather than single commands.
# Example command
ansible localhost -a "touch /tmp/test1"

# Same command, but skips if file exists
ansible localhost -a "touch /tmp/test1 creates=/tmp/test1"

# Delete the file
ansible localhost -a "rm -f /tmp/test1 removes=/tmp/test1"

# Shell module for env variable and output redirection
ansible localhost -m shell -a "echo $PATH > /tmp/file1"

Collecting system information

  • Ansible facts are properties and info about remote systems.
  • The setup module can retrieve facts.
  • Facts may be filtered using the setup module ad-hoc by passing a value for the filter param.
  • Examples:
    • ansible centos2.jm -m setup | less -MN
    • Filtered: ansible centos2.jm -m setup -a "filter=*dist*" | less -MN
    • Create a JSON file per host in "facts" folder: ansible centos -m setup --tree facts

Back to table of contents

File manipulation with ansible

Working with the file and copy modules

  • The file module can be used to create, delete, and modify file properties.
    • Check out ansible-doc file for parameters you can set, including permissions, owner, mod time, etc.
  • The copy module can be used to copy files from the control to the target node or from the file system on the target node.
    • src = location on control node
    • remote_src = location on destination node

Examples

# Create a file. Default location will be home
ansible centos -m file -a "name=testfile state=touch"

# Become root to create a file in a protected location
ansible centos -b -m file -a "name=/root/testfile state=touch"

# Delete the file
ansible centos -b -m file -a "name=/root/testfile state=absent"

# File copy example
ansible centos -m copy -a "src=testile dest=newfile"

Editing file contents with the lineinfile module

  • The lineinfile module allows us to insert a line of text into a file. It can also remove lines of text.
  • The default is to add the line to the end of the file, but you can place it before or after matched text.
  • If the module detects the line in the file already, it will not add it again.
  • Some arguments
    • create=yes: Create if !exists
    • insertafter: Insert after last match specified
    • insertbefore: Insert before last match specified
    • regexp: Replace the matched expression with the line. Cannot be used with insertafter nor insertbefore
  • NOTE: There is a replace module that can make more granular changes using regex, replacing all occurences of a file.

Examples

# If you run the insert commands twice in a row, the second time will report
# SUCCESS and changed: false
ansible centos -m lineinfile -a "path=/home/ansible/testfile line='I am the walrus.' state=present create=yes"

ansible centos -m lineinfile -a "line='I am before the walrus' path=/home/ansible/testfile insertbefore='walrus'"

Downloading files with the get_url module

  • The get_url module allows you to download files via HTTP, HTTPS, and FTP. the destination must be an absolute path.
  • Basic and x509 authentication are supported.
  • Can perform checksum verification.
  • Supports proxy network access.
  • ansible-doc get_url

Examples

ansible centos -m get_url -a "url=http://google.com dest=/home/ansible/google.html"

Working with file archives

  • The archive and unarchive modules can work with various types of file archives (tar, gunzip (default), and zip).

Example

ansible centos -m lineinfile -a "line='test text for file 3' path=/home/ansible/file3 create=yes"

ansible centos -m archive -a "path=/home/ansible/file3 format=zip dest=/tmp/file3.zip"

ansible centos -m unarchive -a "remote_src=yes src=/tmp/file3.zip dest=/tmp"

Back to table of contents

Configuring system users and groups

Creating system users with the user module

  • The user module can be used to create, remove, and modify users.
  • If you remove a user but don't use the remove=yes argument, the user will be removed from /etc/passwd but other artifacts (such as home directory) will remain.
  • Args:
    • append: add user to specified groups
    • generate_ssh_key: duh
    • name: user name
    • state: absent to remove and present to create (default)

Examples

ansible centos -b -m user -a "name=thedude"

ansible centos -b -m user -a "name=thedude state=absent remove=yes"

Working with the group module

  • Similar to user module

Examples

ansible centos -b -m group -a "name=consultants"

ansible centos -b -m user -a "name=thedude group=consultants"

# You wouldn't be able to delete the group while it's the primary group of thedude
ansible centos -b -m user -a "name=thedude group=ansible"

ansible centos -b -m group -a "name=consultants state=absent"

Back to table of contents

Installing software and daemon management

Installing software

  • Depending on the distro, you can use package, yum, and apt.
    • package: will detect which package manager to use. Best practice for mixed distro environment.
  • Ansible cannot handle when packages aren't named the same (e.g., apache2 for Ubuntu vs httpd for CentOS).

Examples

ansible centos -b -m package -a "name=ntpdate state=latest"

Controlling daemons with the service module

  • The service module is compatible with systemd and the older BSD init style of daemon management.

Example

ansible -b -m service -a "name=httpd state=started enabled=yes"

Back to table of contents

Advanced features

Managing long-running commands

  • -B is used to provide a timeout value for Ansible to consider the task failed if it exceeds that value.
  • -P allows you to poll the operation on a set interval.
  • The status may be checked with the async_status module (with playbooks, not ad hoc).

Examples

# timeout of 15 seconds
ansible centos -a "/home/ansible/sleep.sh" -B 15

# Polling interval should be < timeout interval
ansible centos -a "/home/ansible/sleep.sh" -B 60 -P 20

Parallelism in Ansible

  • Ansible uses forks to execute tasks in parallel.
  • Each fork is able to run a task against a target host.
  • The default is to execute five forks.
    • E.g., one command against 5 hosts results in near simultaneous execution on all hosts. If over five hosts are targetted, a fork must be freed for host six.
  • The number of forks used by Ansible may be configured in ansible.cfg or with the -f or --forks flag.
  • More forks = more resources required on control node.

Back to table of contents

Conclusion

Conclusion and next steps

  • Check out the Ansible Playbooks Deep Dive course, part 2 of this course.
  • There's also Git, and DevOps training in general.

Back to table of contents

Examples

Create user, create directory, and move a file from control node to targets

# Create the user accounts noted in /home/ansible/userlist.txt.
ansible dbsystems -b -m user -a "name=consultant"
ansible dbsystems -b -m user -a "name=supervisor"

# Create the directory for the authorized keys
ansible dbsystems -b -m file -a "path=/home/consultant/.ssh state=directory owner=consultant group=consultant mode=0755"
ansible dbsystems -b -m file -a "path=/home/supervisor/.ssh state=directory owner=supervisor group=supervisor mode=0755"

# Copy the authorized_keys file from control node to target nodes
ansible dbsystems -b -m copy -a "src=/home/ansible/keys/consultant/authorized_keys dest=/home/consultant/.ssh owner=consultant group=consultant mode=0600"
ansible dbsystems -b -m copy -a "src=/home/ansible/keys/supervisor/authorized_keys dest=/home/supervisor/.ssh owner=supervisor group=supervisor mode=0600"

# Ensure auditd is enabled and running on all systems.
ansible dbsystems -b -m service -a "name=auditd state=started enabled=yes"
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