handling and killing idle clients in redis

Considering redis is single threaded, it is best if an application maintains a single connection and uses it to query redis, because redis will process all requests one by one, anyways.

Many times in redis, we have to kill the idle connections in redis. This is useful if there is an application which creates a number of connections but does not close them.

There are some ways to avoid the idle connections in redis.

One of way is to set an idle timeout in redis.
This is done by setting the "timeout" value in seconds in redis.conf which requires a redis restart. Below is the entry in redis.conf

#Close the connection after a client is idle for N seconds (0 to disable)
timeout 3600

This can also be done by setting the timeout through config without redis restart by executing the below command.

src/redis-cli CONFIG SET timeout 3600

Considering, the config value set using the method 2 above is lost if the redis restarts, it is important to set it in redis.conf(method1) and then set it using config(method 2) so that redis does not require a restart and also the value persists even after there is a restart.

Note that, by default the value of timeout is 0, ie idle connections are everlasting and are never killed by redis server.

The Catch
The catch here is that the timeout is only applicable for normal clients, not for pub-sub ones, so that a pubsub client will not timeout even though its idle time exceeds the idle timeout defined. This is because the default behavior of pub-sub clients is to wait for events.  This is mentioned here.


Killing clients of a particular type in redis

Sometimes if you want to kill all the clients of a particular type, the below command may come in handy.

# kills all normal clients
src/redis-cli CLIENT KILL TYPE normal

# kills all pub-sub clients
src/redis-cli CLIENT KILL TYPE pubsub

# kills all slave clients
src/redis-cli CLIENT KILL TYPE slave

It is important to note that the above commands should be executed after due consideration. If our redis clients(like Jedis/Lettuce clients in java) reconnect, the above command will kill all connections and valid connections will reconnect, so that the application will be ok.

However if our clients don't reconnect, then we need to manually identify the clients/ip addresses which are expired/need to be terminated, and we need to kill those clients only.


Killing redis connections from an ip address

If we want to kill connections of a particular type from a particular ip address, then we can identify those connections using the CLIENT LIST command in redis, and kill them using the CLIENT KILL command in redis.

The below command will kill all pub-sub connections of a given ip address '10.150.20.30'

redis-cli -h 127.0.0.1 -p 6379 CLIENT LIST | grep 'sub=1' | grep '10.150.20.30' | awk  {'print $2'} | awk -F "=" {'print "CLIENT KILL ADDR " $2'} |  redis-cli -h 127.0.0.1

In the above, "redis-cli -h 127.0.0.1 -p 6379 CLIENT LIST | grep 'sub=1' | grep '10.150.20.30' " will get the pub-sub connections from redis client list command, then get "id=10.150.20.30:port" using awk  {'print $2'} and print client kill ADDR <ip:port> and pass it to redis-cli command.

This will ensure that all those connections satusfying the criteria are killed.

Similar to above, the below command can also be used, but is a bit slower.

redis-cli -h 127.0.0.1 -p 6379 CLIENT LIST | grep '10.150.20.30' | awk  {'print $2'} | awk -F "=" {'print "CLIENT KILL TYPE pubsub addr " $2'} |  redis-cli -h 127.0.0.1

The complete details of the redis client kill command can be found here.

:)