How to run multiple Redis instances on Ubuntu 18.04

notes.md

Create the directory for the new instance

$ sudo install -o redis -g redis -d /var/lib/redis2

Create a new configuration file

$ sudo cp -p /etc/redis/redis.conf /etc/redis/redis2.conf

Edit the new configuration file

$ sudo nano /etc/redis/redis2.conf

pidfile /var/run/redis2/redis-server2.pid
logfile /var/log/redis/redis-server2.log
dir /var/lib/redis2
port 6380

Create new service file

$ sudo cp /lib/systemd/system/redis-server.service /lib/systemd/system/redis-server2.service

Edit the new service file

$ sudo nano /lib/systemd/system/redis-server2.service

ExecStart=/usr/bin/redis-server /etc/redis/redis2.conf
PIDFile=/var/run/redis/redis-server2.pid
RuntimeDirectory=redis2
ReadWriteDireRuntimeDirectory=redis2
ReadWriteDirectories=-/var/run/redis2
Alias=redis2.service

Enable and start the service

$ sudo systemctl enable redis-server2.service
$ sudo systemctl start redis-server2.service

Check status

$ ps aux |grep redis

I'm getting this error:

255584:C 24 Jun 2021 14:44:20.189 # oO0OoO0OoO0Oo Redis is starting oO0OoO0OoO0Oo 255584:C 24 Jun 2021 14:44:20.189 # Redis version=5.0.7, bits=64, commit=00000000, modified=0, pid=255584, just started 255584:C 24 Jun 2021 14:44:20.189 # Configuration loaded 255584:C 24 Jun 2021 14:44:20.189 * supervised by systemd, will signal readiness 255584:M 24 Jun 2021 14:44:20.190 # Can't open the append-only file: Read-only file system

Any idea how to fix this?

Thanks.

There is small mistake. Pid file path should be: PIDFile=/var/run/redis2/redis-server2.pid in service file

Hi, there is some mistake in this line here right ?
ReadWriteDireRuntimeDirectory=redis2

System service should be modified without changing directory. Here's the difference that works:
@@ -8 +8 @@
-ExecStart=/usr/bin/redis-server /etc/redis/redis.conf
+ExecStart=/usr/bin/redis-server /etc/redis/redis-cache-server.conf
@@ -10 +10 @@
-PIDFile=/run/redis/redis-server.pid
+PIDFile=/run/redis/redis-cache-server.pid
@@ -46 +46 @@
-Alias=redis.service
+Alias=redis-cache-server.service

System service should be modified without changing directory. Here's the difference that works: @@ -8 +8 @@ -ExecStart=/usr/bin/redis-server /etc/redis/redis.conf +ExecStart=/usr/bin/redis-server /etc/redis/redis-cache-server.conf @@ -10 +10 @@ -PIDFile=/run/redis/redis-server.pid +PIDFile=/run/redis/redis-cache-server.pid @@ -46 +46 @@ -Alias=redis.service +Alias=redis-cache-server.service

If the directory RuntimeDirectory has not been changed, executing systemctl stop redis2 leads to the disappearance of the unix socket and the pid file of the first instance of Redis because "runtime directory is cleaned up automatically after use". At the same time, systemctl status redis and pid aux | grep redis says that everything is fine - the systemd unit is active and the process exists, but there is no unix socket of the first instance of Redis. That's why it's crucial to change RuntimeDirectory. ReadWriteDirectories should be changed for different directories as well.

BTW, I think it's better to store everything in different directories: pid, unixsocket, logfile, dir (working directory), and the config too, especially since "redis-server can write to its own config file when in cluster mode". It's safer.