Multiple Redis databases on Debian

Occasionally you may want to run multiple Redis database on the same host.

Redis has a concept of databases, however these are less like a traditional database, and more like a namespace. Redis databases have a number of drawbacks:

• Redis databases have a number (typically 0-15) rather than a name
• Configuration, including password, are shared by all Redis databases
• Redis databases do not work in a Redis cluster¹
• Pub-sub messaging ignores Redis databases²
• ACLs ignore Redis databases³

An interesting feature that Redis databases do have is that they can be swapped instantly using the SWAPDB⁴ command. Although I haven’t found a use case for this yet.

In order to have multiple real Redis databases simply run multiple instances of Redis server on the host.

Running multiple instances on Debian is documented⁵, but this documentation is a bit hard to find, so here are the steps:

Copy the file /etc/redis/redis.conf to redis-myinstance.conf

cp /etc/redis/redis.conf /etc/redis/redis-myinstance.conf 

Change the following directives in redis-myinstance.conf:

When comparing the original and myinstance configuration

diff -u0 /etc/redis/redis.conf /etc/redis/redis-myinstance.conf

The difference should look something like

--- redis.conf
+++ redis-myinstance.conf
@@ -91 +91 @@
-port 6379
+port 6380
@@ -108 +108 @@
-# unixsocket /var/run/redis/redis-server.sock
+# unixsocket /var/run/redis-myinstance/redis-server.sock
@@ -247 +247 @@
-pidfile /var/run/redis/redis-server.pid
+pidfile /var/run/redis-myinstance/redis-server.pid
@@ -260 +260 @@
-logfile /var/log/redis/redis-server.log
+logfile /var/log/redis/redis-server-myinstance.log
@@ -342 +342 @@
-dbfilename dump.rdb
+dbfilename dump-myinstance.rdb

In addition change any other configuration directives you like. I strongly recommend setting requirepass to a strong password, even if you intend to only use Redis locally.

Now use systemd’s instantiated service feature to enable and start your instance

systemctl enable redis-server@instance.service -–now

You should now have another Redis instance running, waiting to be used. Check its status using

systemctl status redis-server@instance.service

Now connect using your favorite Redis client, e.g. when using Java from the same machine use the following URL

redis://password@localhost:6380/

Enjoy your new Redis instance.