TPA custom commands v23

You can define custom commands that perform tasks specific to your environment on the instances in a TPA cluster.

You can use this mechanism to automate any processes that apply to your cluster. These commands can be invoked against your cluster directory, like any built-in cluster management command. Having a uniform way to define and run such processes reduces the likelihood of errors caused by misunderstandings and operator error, or process documentation that was correct in the past, but has drifted away from reality since then.

Writing Ansible playbooks means that you can implement arbitrarily complex tasks; following the custom command conventions means you can take advantage of various facts that are set based on your config.yml and the cluster discovery tasks that TPA performs, and not have to think about details like connections, authentication, and other basic features.

This makes it much easier to write resilient, idempotent commands in a way that ad-hoc shell scripts (could be, but) usually aren't.

Quickstart

• Create commands/mycmd.yml within your cluster directory
• Run tpaexec mycmd /path/to/cluster

Example

Here's an example of a command that runs a single command on all instances in the cluster. Depending on the use-case, you can write commands that target different hosts (e.g., hosts: role_postgres to run only on Postgres instances), or run additional tasks and evaluate conditions to determine exactly what to do.

---
# Always start with this
- import_playbook: "{{ tpa_dir }}/architectures/lib/init.yml"
  tags: always

- name: Perform custom command tasks
  hosts: all
  tasks:
  - name: Display last five lines of syslog
    command: tail -5 /var/log/syslog
    become_user: root
    become: yes

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• Quickstart
• Example