docs(redict): document migration to redict

Related to packit#561

Signed-off-by: Matej Focko <[email protected]>

docs/deployment/specifics/redict.md

@@ -0,0 +1,48 @@
+---
+title: Redict
+---
+
+## Seamless migration between providers
+
+We have tested a seamless migration from Redis to Redict on our production
+deployment. To reproduce:
+
+1. We have deployed Redict to our production cluster.
+2. Using remote shell and `redict-cli` run:
+
+   ```sh
+   replicaof redis 6379
+   ```
+
+   This converts the Redict instance into a read-only replica of the Redis.
+
+3. After the data exchange is done, change **all** references in variables to
+   redis to point to the new hostname, in this case `redis → redict`.
+4. Simultaneously run the deployment with the changed hostnames and via
+   `redict-cli` run:
+
+   ```sh
+   replicaof no one
+   ```
+
+   to make the redict deployment the primary one.
+
+5. (optional) For safety reasons and easier rollback, it's possible to convert
+   the former Redis deployment into a replica of Redict, just in case it needs
+   to be reverted without loss of data. For this you can run in `redis-cli`:
+
+   ```sh
+   replicaof redict 6379
+   ```
+
+:::warning References to Redis
+
+Redis is being referenced from:
+
+- `packit-service` (API endpoint)
+- `packit-service-fedmsg` (Fedora Messaging listener)
+- `packit-service-beat` (triggers periodic tasks)
+- `packit-worker` (runs the jobs provided by API, Fedora Messaging and “beat”)
+- `flower` (monitoring of the Celery queues)
+
+:::