A simple ruby gem for adding read only maintenance mode to your Rails / Rack applications.

When read only mode is enabled, all non GET / HEAD requests will be rejected with a 503 Service Unavailable response. Additionally the 503 response will be given in case a GET request would raise a PG::ReadOnlySqlTransaction error.

Add the line to your application's Gemfile:

gem "read_only_mode"

Read only mode is enabled via environment variables. There are two options, either:

Set READ_ONLY_MODE=true

Or...

Set PGOPTIONS="-c default_transaction_read_only=on" (or any other string containing default_transaction_read_only=on).

The PGOPTIONS approach is recommended for applications using Postgres as this will prevent any write queries from being executed.

Rails applications will automatically use the middleware via a Railtie. For other Rack applications, you can add the middleware manually:

use ReadOnlyMode::Middleware if ReadOnlyMode.enabled?

You can customize the HTML / JSON responses returned when read only mode is enabled via some simple setters:

ReadOnlyMode.html_response = File.read("path/to/your/read_only.html")
ReadOnlyMode.json_response = { error: "Maintenance in progress" }.to_json