How to Solve 'Hostname Does Not Match The Server Certificate' Issue in Amazon S3 with Rails

How to Solve ‘Hostname Does Not Match The Server Certificate’ Issue in Amazon S3 with Rails

If you’re a Rails developer working with Amazon S3, you may have come across this error: OpenSSL::SSL::SSLError: hostname does not match the server certificate. This can be a frustrating problem to encounter, especially if you’re not familiar with SSL certificates or how they work. In this guide, I’ll explain what this error means, why it occurs, and how you can resolve it.

What Is OpenSSL::SSL::SSLError?

Before diving into the solution, let’s first understand what OpenSSL::SSL::SSLError is. SSL (Secure Sockets Layer) is a protocol that provides secure communication over a network. OpenSSL is a widely used open-source implementation of the SSL protocol. When Ruby encounters an issue with this protocol, it raises an OpenSSL::SSL::SSLError.

This particular error is thrown when the hostname provided in the URL does not match the one in the server’s SSL certificate. It’s a security measure to prevent Man-in-the-Middle (MitM) attacks.

Why Does This Error Occur with Amazon S3 and Rails?

Rails uses the aws-sdk gem to interact with S3. When you make a request to an S3 bucket, the gem initiates an HTTPS connection to the S3 server using the hostname of the bucket.

The problem arises if your bucket name contains periods (.) - for example, my.bucket.name. In this case, the SSL certificate for https://my.bucket.name.s3.amazonaws.com/ is issued to *.s3.amazonaws.com, and it doesn’t cover my.bucket.name.s3.amazonaws.com because wildcard certificates only cover one level of subdomains.

How to Solve the Issue

There are two main ways to solve this issue:

1. Rename Your Bucket

The simplest solution is to rename your bucket so it doesn’t contain any periods. For example, you could rename my.bucket.name to my-bucket-name. This way, there won’t be any mismatch between the hostname in the URL and the one in the SSL certificate.

# config/initializers/aws.rb

Aws.config.update({
  region: 'us-west-2',
  credentials: Aws::Credentials.new('YOUR_ACCESS_KEY', 'YOUR_SECRET_KEY'),
  s3: { bucket: 'my-bucket-name', force_path_style: true },
})

2. Use Path-Style Access

If you can’t change the bucket name, you can switch to using path-style access instead of subdomain-style access. Instead of using https://my.bucket.name.s3.amazonaws.com/, you would use https://s3.amazonaws.com/my.bucket.name.

Amazon deprecated path-style access for new buckets from 2020, but any bucket created before this date still supports it. You can enable it in the aws-sdk configuration:

# config/initializers/aws.rb

Aws.config.update({
  region: 'us-west-2',
  credentials: Aws::Credentials.new('YOUR_ACCESS_KEY', 'YOUR_SECRET_KEY'),
  s3: { bucket: 'my.bucket.name', force_path_style: true },
})

Conclusion

SSL errors like OpenSSL::SSL::SSLError: hostname does not match the server certificate can be tricky to diagnose and resolve, but with a solid understanding of why they occur and how SSL certificates work, you can quickly get your Rails app and Amazon S3 working together smoothly again.

Whether you choose to rename your bucket or switch to path-style access, remember that the key is to ensure that the hostname in your URL matches the one in the SSL certificate. Happy coding!

Keywords: Amazon S3, Rails, OpenSSL::SSL::SSLError, SSL Certificate, aws-sdk, bucket name, path-style access, subdomain-style access, hostname, server certificate, rename bucket, Man-in-the-Middle attacks.

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