How to Fix bundle exec rake db:migrate Hanging on Amazon EC2 and RDS

How to Fix bundle exec rake db:migrate Hanging on Amazon EC2 and RDS

Hello fellow data scientists and software engineers! We often confront a common issue when deploying Ruby on Rails applications on AWS’s EC2 instances and RDS databases. You might have encountered a situation where running bundle exec rake db:migrate seemingly hangs indefinitely. This article will help you understand why this occurs and how to resolve it.

What is bundle exec rake db:migrate?

Before diving into the solution, let’s understand the command bundle exec rake db:migrate. It’s a command specific to Ruby on Rails applications. rake is a Ruby build program that allows you to script tasks, and db:migrate is one such task that manages your database schema and applies migrations.

bundle exec is a Bundler command that ensures the command rake db:migrate is run in the context of the current bundle (the app’s environment). In simpler terms, it guarantees that you’re using the correct set of gems specified in your Gemfile.

Why does bundle exec rake db:migrate hang?

The hanging of bundle exec rake db:migrate on EC2 and RDS is typically due to one of two reasons: network issues or database locks.

1. Network Issues: You might have a misconfigured security group that is blocking the necessary traffic between your EC2 instance and RDS database.

2. Database Locks: It’s possible that a previous migration was interrupted and left a lock in your database. This lock prevents new migrations from running.

How to solve hanging issues

Solution 1: Checking Network Configuration

To ensure your EC2 instance can communicate with your RDS database, follow these steps:

1. Go to your RDS instance on the AWS Console and check the security group(s) associated with it.

2. For each security group, check the inbound rules. There should be an entry which allows traffic from your EC2 instance’s security group.

3. If the rule doesn’t exist, add a new inbound rule. Set Type to “All traffic”, and for Source, specify the ID of your EC2 instance’s security group.

Solution 2: Resolving Database Locks

If network configurations are correct, check for database locks. Here’s how to do it:

1. Connect to your RDS database directly. You can use a SQL client like MySQL Workbench or DBeaver, or mysql command-line if it’s installed on your EC2 instance.

2. Run the following query to check for locks: SHOW FULL PROCESSLIST;

3. If you see a migration process with the state “Locked”, that’s your culprit. Note the ID of the process.

4. To kill the process, run: KILL <process_id>;, replacing <process_id> with the ID from step 3.

After removing the lock, try running bundle exec rake db:migrate again.

Conclusion

While deploying Ruby on Rails applications on AWS EC2 and RDS, bundle exec rake db:migrate hanging indefinitely can be a common issue. However, by ensuring correct network configurations and handling database locks, you can resolve this issue efficiently. Remember to always check your security groups and regularly monitor your database to avoid such hang-ups in the future.

Keep coding, and let’s keep solving problems together!

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