How to Fix Redis Error After Migration on AWS EC2

Migrating your EC2 environment from Amazon Linux to CentOS 7 can be a rewarding yet challenging process. Each operating system has its nuances, and this becomes even more evident when setting up applications like Redis. If you're encountering issues with Redis after migration, particularly with its service status showing as “failed” in systemctl, you're not alone. Let’s dive into a step-by-step approach to troubleshoot and resolve this issue.

Background of the Issue

In your migration journey, you’ve managed to set up most services on CentOS 7, but Redis has presented a unique challenge. The redis.service shows a status failure in systemctl, specifically with errors related to ExecStart and ExecStop. To add to the confusion, your Redis log file (redis.log) is created but remains empty, which typically indicates that Redis is failing early during the startup process.

Steps to Troubleshoot Redis Service Failure on CentOS 7

Here are some steps you can take to troubleshoot and potentially resolve this issue.

1. Verify Redis Installation and Configuration Files

Start by double-checking that Redis is correctly installed and that the configuration file is accessible:

• Redis Installation: Confirm Redis is installed by running:

  
  $ redis-server --version
  

• Configuration File Path: Verify the configuration file path specified in the Redis service file. By default, Redis looks for /etc/redis.conf, but any discrepancy here can prevent the service from starting.

2. Check Redis Service Configuration (redis.service)

Inspect the redis.service file located in /usr/lib/systemd/system/redis.service or any custom override files (such as /etc/systemd/system/redis.service.d/limit.conf) to ensure no conflicting or incorrect configurations are set.

• Run:

  
  $ cat /usr/lib/systemd/system/redis.service
  $ cat /etc/systemd/system/redis.service.d/limit.conf
  

• Look specifically at ExecStart and ExecStop lines. Ensure ExecStart points to the correct path for redis-server and ExecStop for redis-shutdown.

3. Test Redis Configuration for Errors

Before attempting to start the Redis service, it’s useful to test the Redis configuration file directly. Redis has a built-in utility for this:

$ redis-server /etc/redis.conf --test-memory

Any errors related to the configuration file will appear here, helping you catch issues early.

4. Examine System Logs and SELinux

Since your Redis log file is empty, checking system logs for more insights could help pinpoint the issue. SELinux policies in CentOS 7 can sometimes block Redis from accessing certain files or starting as a service.

• System Logs:

  
  $ journalctl -xe
  

  Look for any entries related to redis.service for specific errors or clues.

• SELinux: Temporarily disable SELinux to see if it’s causing the issue:

  
  $ sudo setenforce 0
  

  After disabling SELinux, try restarting the Redis service:

  
  $ sudo systemctl restart redis.service
  

If Redis starts successfully with SELinux disabled, consider creating a policy to allow Redis to run with SELinux enabled.

5. Review Resource Limits

In CentOS, default system limits can be restrictive. Redis often requires higher limits on open files and memory, which you can set in limit.conf or /etc/security/limits.conf. Typical adjustments include:

* soft nofile 65536
* hard nofile 65536

Once updated, reload the limits by logging out and logging back in, then attempt to restart Redis.

6. Restart and Monitor Redis

Try restarting the Redis service after making adjustments:

$ sudo systemctl daemon-reload
$ sudo systemctl restart redis.service

Check the service status again to see if Redis is now active:

$ sudo systemctl status redis.service

7. Final Steps: Enable Redis on Boot

Once the Redis service is running correctly, make sure it’s enabled to start automatically after reboots:

$ sudo systemctl enable redis

Wrapping Up

Redis issues on CentOS 7 often come down to configuration paths, SELinux policies, or resource limits. By following these steps, you should be able to pinpoint the problem and get your Redis instance running smoothly on CentOS 7. If the issue persists, checking the broader CentOS and Redis communities for specific compatibility tips might also be useful.

Happy troubleshooting, and best of luck with your migration!