Fixing PM2 'Process Not Found' Errors In GitLab CI Deployments

by TheNnagam 63 views

Hey guys! Ever run into the frustrating "Process or Namespace not found" error when trying to deploy your Node.js app with PM2 via GitLab CI? Yeah, it's a common headache. You're probably scratching your head, especially when whoami in your CI script shows the correct user, the same one that started PM2 initially. Don't worry, we're gonna dive deep into this and get your deployments running smoothly. This article will help you understand the root causes and provide actionable solutions to fix PM2 deployment issues in GitLab CI pipelines, covering Node.js, Ubuntu 18.04, and PM2.

The Problem: PM2 and GitLab CI Disconnect

So, what's going on? You've got your Node.js app, you're using PM2 for process management, and you're deploying with GitLab CI. Everything should be peachy, right? Not always. The core problem often boils down to a disconnect between how PM2 is started and how GitLab CI runs your deployment scripts. Specifically, PM2 processes are often tied to the user context in which they're started. When your CI pipeline executes, it might be running under a different user or a different environment than the one that initially launched PM2. This means that when your deployment script tries to restart your app using pm2 restart appname, PM2 can't find the process because it doesn't recognize the user or the context.

This is where things get tricky. You might be seeing the correct user with whoami during the deployment script's execution, but that doesn't necessarily mean PM2 is aware of that user's context. The PM2 process might have been started by a different user during a previous build or deployment, or even manually before you set up the CI/CD pipeline. The error message is the telltale sign: "Process or Namespace not found". It means PM2 can't locate the process you're trying to manage, even though you think it should be there.

Another critical aspect to consider is the working directory of your PM2 process and the CI script. If the working directory where PM2 was started is different from where your deployment script is running, PM2 might not be able to find the process definition or the app files. Ensuring consistency in the working directories is crucial. Sometimes, the issue isn't a user mismatch, but an environment mismatch. Are you setting up the environment variables correctly for your PM2 process to run? Are the same environment variables available during your CI pipeline run?

This also relates to how PM2 stores its process configuration. PM2 uses a configuration file (like a JSON file) to keep track of the processes it manages. If there's a problem with this configuration file (e.g., it's corrupted, or the script doesn't have permissions to access it), then PM2 might fail to find the process.

Ultimately, understanding these nuances is key to diagnosing the problem and finding the right solution. Let's dig into some troubleshooting steps and fixes.

Troubleshooting Steps: Uncovering the Root Cause

Before diving into fixes, let's nail down what's causing the problem. Here are some key troubleshooting steps:

  1. Verify the User Context: This is the most crucial step. Double-check that the user running your deployment script is the same user that started the PM2 process. Inside your GitLab CI script, add the following commands:

    whoami
sudo -u <pm2_user> whoami # Replace <pm2_user> with the user that started PM2. Often 'ubuntu' or your deployment user.
pm2 list # Run this to see if the process is visible.

    The output of pm2 list will show you the user that started the PM2 process. If the user from whoami doesn't match the one from pm2 list, then you've found a major clue.

  2. Check PM2's Process List: Run pm2 list inside your CI script. This will show you all the processes currently managed by PM2. If your app isn't listed, that confirms the "Process not found" error. Examine the output for any errors or warnings. Pay close attention to the status of your app. This command helps you to verify the status of the process, and also shows the user that owns the process.

  3. Inspect PM2 Logs: PM2 keeps detailed logs. Check them for error messages. Use pm2 logs in your CI script, or examine the log files directly. Logs are usually located in the .pm2 directory in your home directory, often under /home/<user>/.pm2/logs/. Look for any clues about why the process is failing to start or restart. These logs often provide a goldmine of information about what's going wrong. The log files might contain errors related to file permissions, environment variables, or other configuration issues.

  4. Verify the Working Directory: Ensure your deployment script is running in the same directory where your app's main file is located. If your PM2 process was started from a different directory, it won't be able to find your app. You can use the pwd command to verify the current working directory in your CI script.

  5. Environment Variables: Carefully examine your environment variables. Ensure that all the necessary environment variables are set correctly both in your CI pipeline and in your PM2 configuration. Any discrepancies here can cause problems. Incorrect environment variables can lead to the app failing to start or behave as expected.

  6. PM2 Configuration: Review your PM2 configuration file (if you're using one). Ensure the script path points to the correct entry point of your Node.js application. Also, make sure that any other relevant settings, such as cwd (current working directory), are correctly configured.

By systematically working through these steps, you should be able to narrow down the cause of the "Process or Namespace not found" error.

Solutions: Fixing the PM2 Deployment

Now for the good stuff: How to fix the problem! Here's a breakdown of the most common solutions.

1. Using the Correct User

If the user mismatch is the issue, the simplest solution is to ensure your CI script runs commands as the user that owns the PM2 process. There are a few ways to achieve this.

  • sudo -u <pm2_user>: As shown above, you can use sudo -u <pm2_user> pm2 restart appname in your CI script. Replace <pm2_user> with the correct user (e.g., ubuntu). This executes the pm2 restart command as the specified user. This approach is straightforward and generally works well if you have sudo configured correctly.

  • Environment Variables & SSH Keys: If you're deploying to a remote server, use SSH keys to connect to the server as the PM2 user. This eliminates the need for password-based authentication and gives the CI/CD pipeline access to the appropriate user context.

    # Example of using SSH keys in your .gitlab-ci.yml
deploy:
  stage: deploy
  before_script:
    - 'which ssh-agent || ( apt-get update -y && apt-get install openssh-client -y )'
    - eval $(ssh-agent -s)
    - ssh-add <(echo "$SSH_PRIVATE_KEY")
    - mkdir -p ~/.ssh
    - chmod 700 ~/.ssh
    - ssh-keyscan <your_server_ip> >> ~/.ssh/known_hosts
    - chmod 644 ~/.ssh/known_hosts
  script:
    - ssh <pm2_user>@<your_server_ip> "cd /path/to/your/app && pm2 restart appname"
  # ... other configurations

    Make sure you have set the SSH private key in GitLab CI/CD variables.

2. Ensuring Persistence

  • Saving PM2 Process List: Ensure PM2 is configured to save its process list. This is crucial for restarts and managing processes across server reboots. Run pm2 startup to generate the startup script, and then execute the output from the command as the PM2 user. The startup script ensures that PM2 automatically restarts your processes when the server reboots. This command ensures PM2 remembers your processes. PM2 will generate a startup script tailored to your system (e.g., systemd or init.d). You can then run this script to configure PM2 to start on system boot. This also handles user context and ensures PM2 processes start correctly.

    # Inside your CI script, as the correct user:
pm2 startup # Follow the instructions it outputs. Often involves running a command like this:
# sudo env PATH=$PATH:/usr/bin /usr/lib/node_modules/pm2/bin/pm2 startup systemd -u <pm2_user> --hp /home/<pm2_user>

3. Absolute Paths and Configuration

  • Use Absolute Paths: Always use absolute paths in your PM2 configuration and deployment scripts. This helps avoid confusion about the working directory. In your PM2 configuration file (e.g., ecosystem.config.js or ecosystem.config.cjs), specify the full path to your app's entry point.

    // Example ecosystem.config.js
module.exports = {
  apps: [{
    name: 'appname',
    script: '/path/to/your/app/index.js',
    // ... other configurations
  }]
};

  • Configure PM2: If you're using a configuration file, make sure it's located in a place where your CI script can access it. Use the pm2 start ecosystem.config.js command. The path to the config file should also be an absolute path. Verify that the correct configuration file is being used during deployment.

4. Addressing Permissions

  • File Permissions: File permissions can also cause the "Process not found" error, particularly if the user running the deployment script doesn't have the necessary permissions to access the app files, the PM2 configuration files, or the logs. Make sure the deployment user has read and execute permissions on all the files and directories required by your application.

    #Example to fix permissions:
sudo chown -R <pm2_user>:<pm2_user> /path/to/your/app
sudo chmod -R 755 /path/to/your/app # Or more restrictive if your app needs it.

5. Deployment Strategies

  • Zero-Downtime Deployments: Consider using strategies like zero-downtime deployments. This involves deploying a new version of your app alongside the existing one and then switching traffic. This can mitigate potential issues during the restart process. PM2 supports this through the pm2 deploy command. This can also help you avoid downtime during the deployment.

Putting It All Together: A Sample GitLab CI/CD Configuration

Here's an example .gitlab-ci.yml file, illustrating how to combine these solutions for a basic Node.js deployment. Remember to adjust the paths and user to match your specific setup. This is just a starting point, and you might need to customize it further based on your app's requirements.

stages:
  - build
  - deploy

build_job:
  stage: build
  image: node:18 # Or your preferred Node.js version
  script:
    - npm install
    - npm run build # If you have a build step
    - npm test
  artifacts:
    paths:
      - dist # Or your build output directory

deploy_job:
  stage: deploy
  image: ubuntu:18.04 # Or your preferred Ubuntu version
  before_script:
    - apt-get update -y && apt-get install -y --no-install-recommends openssh-client # Install SSH client
    - mkdir -p ~/.ssh
    - chmod 700 ~/.ssh
    - 'which ssh-agent || ( apt-get update -y && apt-get install openssh-client -y )'
    - eval $(ssh-agent -s)
    - ssh-add <(echo "$SSH_PRIVATE_KEY")
    - ssh-keyscan <your_server_ip> >> ~/.ssh/known_hosts
    - chmod 644 ~/.ssh/known_hosts
  script:
    - ssh <pm2_user>@<your_server_ip> "cd /path/to/your/app && git pull origin main && npm install && pm2 restart appname --update-env"
  environment:
    name: production
    url: http://your-app-url.com
  only:
    - main # Or your deployment branch

Important Notes:

  • Replace Placeholders: Make sure to replace the placeholder values (e.g., <pm2_user>, <your_server_ip>, /path/to/your/app, your-app-url.com, and main) with your actual configuration.
  • SSH Keys: Set the SSH_PRIVATE_KEY variable in your GitLab project's settings (Settings -> CI/CD -> Variables). Make sure it's masked if you don't want it to be displayed in the logs.
  • PM2 User: Ensure that the user you specify in <pm2_user> has the correct permissions and access to your application files and directories.
  • Environment: If your app relies on any environment variables, make sure they are set correctly on the server. You can either set them directly in the server environment or use the --update-env flag with pm2 restart.

Conclusion: Deploying with Confidence

Guys, successfully deploying Node.js apps with PM2 and GitLab CI involves understanding the interplay of users, permissions, and environments. The "Process or Namespace not found" error is a common hurdle, but by systematically troubleshooting and applying the solutions discussed in this guide, you can confidently deploy your apps. Remember to always double-check the user context, verify your PM2 configuration, and ensure that your CI script has the necessary access to your application files and the server. Following these steps will significantly improve your deployments and make your life much easier. Happy coding, and happy deploying!