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redismaster-slave
Ayaz Pasha
Ayaz Pasha

Reputation: 1055

Redis DB Master Slave set up

I have installed Redis for my nodeJS application and configured it to be a slave for another instance of Redis DB running on a different server. Can I have the same instance (different DB) of Redis (running as slave) act as Master for locally installed application?

Thanks in advance

Upvotes: 3

Views: 3510

Answers (1)

Didier Spezia
Didier Spezia

Reputation: 73226

Yes, you can, but with a big caveat.

Any slave instance can be master of one or several other instances. So you can imagine daisy chaining slaves and build a hierarchical replication system.

Now, my understanding is you don't need your slave to feed another Redis instance, but just allow an application to perform read/write operations in another database of the slave instance.

To allow it, you need to set the value of the slave-read-only parameter to "no" in the slave configuration:

# You can configure a slave instance to accept writes or not. Writing against
# a slave instance may be useful to store some ephemeral data (because data
# written on a slave will be easily deleted after resync with the master) but
# may also cause problems if clients are writing to it because of a
# misconfiguration.
#
# Since Redis 2.6 by default slaves are read-only.
#
# Note: read only slaves are not designed to be exposed to untrusted clients
# on the internet. It's just a protection layer against misuse of the instance.
# Still a read only slave exports by default all the administrative commands
# such as CONFIG, DEBUG, and so forth. To a limited extend you can improve
# security of read only slaves using 'rename-command' to shadow all the
# administrative / dangerous commands.
slave-read-only no

Now, all the write operations you will run on this instance will be ephemeral. If the link is lost between the master and the slave, the slave will completely synchronize again to the master. All the data you have set on the slave will be lost. If you stop and restart the slave, you will also loose all the ephemeral data.

It may or may not suit your needs.

There is no way to parameter the synchronization (or the persistence options) at the database level. You cannot tell Redis to synchronize a given database, and not another one. Configuration always applies at the instance level.

Upvotes: 4

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