using pm2 with ansible - node.js

Question

I am trying to start a node program using pm2 via ansible. The problem is that the pm2 start command is not idempotent under ansible. It gives error when run again.
This is my ansible play
- name: start the application
become_user: ubuntu
command: pm2 start app.js -i max
tags:
- app
Now if i run this the first time then it runs properly but when i run this again then i get the error telling me that the script is already running.
What would be the correct way to get around this error and handle pm2 properly via ansible.

Answer 1

Before starting the script you should delete previous, like this:
- name: delete existing pm2 processes if running
command: "pm2 delete {{ server_id }}"
ignore_errors: True
become: yes
become_user: rw_user
- name: start pm2 process
command: 'pm2 start -x -i 4 --name "{{server_id}}" server.js'
become: yes
become_user: rw_user
environment:
NODE_ENV: "{{server_env}}"

Answer 2

I would use
pm2 reload app.js -i max
It will allow you to reload configuration ;-)

Answer 3

I ended up on this page looking for a solution to start PM2 multiple times when I rerun my playbook. I also wanted PM2 to reload the server when it was already running and pickup the new code I might have deployed. It turns out that PM2 has such an interface:
- name: Start/reload server
command: '{{path_to_deployed_pm2}} startOrReload pm2.ecosystem.config.js'
The startOrReload command requires a so-called "ecosystem" file to be present. See the documentation for more details: Ecosystem File.
This is a minimal pm2.ecosystem.config.js that is working for me:
module.exports = {
apps : [{
script: 'app.js',
name: "My app"
}],
};

Answer 4

Here we can use the "register" module to perform a conditional restart/start.
register the output of following command:
shell: pm2 list | grep <app_name> | awk '{print $2}'
register: APP_STATUS
become: yes
and the use APP_STATUS.stdout to make a conditional start and restart tasks. This way we don't need a pm2 delete step.