Using Cluster Commands for AutoPilot – AutoPilot

Using the 'Cluster' Command

The cluster command is a tool for managing and orchestrating operations across a system or a set of systems. It allows you to execute commands on different roles. This document will guide you through the basic usage of the cluster command, focusing on the exec subcommand.

Core Functionality

The cluster command, in essence, enables you to run commands on remote systems. The exec subcommand is particularly useful for executing specfic commands on designated roles, such as web servers, database servers, or cache servers.

The list Subcommand

The list command simply shows all nodes in the cluster.

The `exec` Subcommand

The exec subcommand is used to execute a command on a specified role. The basic syntax is as follows:

cluster exec --role <role> sudo systemctl <action> <service>

Let's break down the components:

cluster exec: This is the primary command and subcommand.
--role <role>: This option specifies the role on which the command should be executed. Replace <role> with the actual role name (e.g., web, database, cache).
sudo: This ensures the systemctl command is executed with the necessary administrative privileges.
systemctl: This is a utility for managing system services in a Linux environment.
<action>: This specifies the action you want to perform on the service (e.g., start, stop, restart, reload, daemon-reload).
<service>: This is the name of the service you want to manage (e.g., nginx, mysql, varnish).

Examples

Here are a few examples to illustrate how to use the cluster exec command:

Restarting a web service:

To restart the Nginx web server on the web role, you would use the following command:
```
cluster exec --role  web -- sudo systemctl restart nginx
```
This command instructs the system to restart the Nginx service on the system(s) designated as the web role.
Restarting a caching service:

To restart the Varnish cache service on the varnish role, the command would be:
```
cluster exec --role varnish -- sudo systemctl restart varnish
```
This ensures that the caching service is restarted, potentially clearing the cache and applying any configuration changes.
Restarting a database service:

To restart the database service on the database role:
```
cluster exec --role database -- sudo systemctl restart mysql
```
This command allows you to manage the database service, ensuring it is running correctly.

Key Considerations

Roles: Ensure that you specify the correct role name. Roles are typically defined in your cluster's list of servers.
Permissions: The sudo command is crucial for performing actions that require elevated privileges.
Services: Use the correct name of the service you intend to manage.

By understanding these concepts and utilizing the cluster exec command effectively, you can streamline system administration tasks, manage services across your infrastructure, and ensure the smooth operation of your applications.