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KeyDB on Fly

KeyDB is a multithreaded fork of Redis designed for high performance on multi-core servers.

KeyDB also supports a multimaster mode which is uniquely suited to deployment on Fly. This mode does not currently enforce strong consistency, but it's useful for a few scenarios today.

Performant global cache

We've written about using standard Redis replicas that can accept writes both from clients and their primary.

Keydb multimaster provides a similar last-write-wins guarantee. So it's useful for caching and does not require targeting a specific instance to invalidate a cache item.

Distributed pub/sub

This setup also supports broadcasting pub/sub events to clients connected to other KeyDB peers using the standard Redis Pub/Sub commands.

KeyDB offers no additional guarantees on deliverability nor ordering of messages. Otherwise, any existing software using Redis pub/sub should work in a multimaster setup.


Get the Fly CLI and a Fly account.

Then, clone this repo and run fly launch. Don't deploy yet - we need to do a bit more setup.

By default, this configuration enables authentication on KeyDB. So let's set a password:

fly secrets set KEYDB_PASSWORD=password

Now let's add storage volumes in Chicago and Amsterdam for KeyDB persistent storage.

fly volumes create keydb_server --region ord
fly volumes create keydb_server --region ams

Now we're ready to deploy!

fly deploy

We can keep track of what's going on with fly logs.

Finally, we'll want to deploy an application in the same regions and connect to the region-local KeyDB.

That can be done by building the instance hostname using the region and application name. For example, the Chicago instance is available at redis://password:password@ord.multimaster-keydb-example.internal.

Check out our example Rails app using Anycable to broadcast websocket messages globally.