Will hostnames be supported ?

[jichilee]

I see "Hostnames are not supported. IPs only." in Redis-trib by using hostnames fails to join cluster #2071, I want to know if hostnames will be supported?
Sometime the IPs are not the best way.

[antirez]

Here the feature request is not clear since there is something that may be supported, and something that may be never supported:

1. Possibly supported: redis-trib resolving names provided, but configuring the cluster using IPs.
2. Never going to be supported in the short timeframe: Redis Cluster itself registering node addresses as hostnames.

However about 2 note that Redis Cluster is able to detect addresses switches of nodes and auto-reconfigure.

[baptistedonaux]

What's the feature's state ? Thx

[allanwax]

@antirez Could you explain more about 'However about 2 note that Redis Cluster is able to detect addresses switches of nodes and auto-reconfigure' and how if all nodes in the cluster have new addresses, how this would be communicated to the other nodes. The problem I see is that while any particular node can examine its nodes.conf file and detect the change, the ip addresses of the other nodes in the nodes.conf file are invalid and communicating with them will fail. Is there some other underlying mechanism for walking the network to detect other cluster nodes on it and check to see if any of them (based upon their id) have changed?

[badboy]

@allanwax It won't work if all of them change their address, exactly because then no node knows how to reach another node. But it works if one node changes its address and connects to an existing node.

[olljanat]

@antirez time is going forward and world is changing so I just wanted to check that is this still the case or would it be possible finally get hostnames support to Redis?

Never going to be supported in the short timeframe: Redis Cluster itself registering node addresses as hostnames.

I'm trying to make Redis Cluster working on Docker Swarm. Initial connection actually works already using hostnames (or Docker service names actually) but then Redis will update IP addresses to config files. I really would like to avoid setting up static IPs for these containers.

[drnybble]

@olljanat You can use the announce-ip option and supply the Virtual IP of the service

[martin-wong]

@olljanat You can use the announce-ip option and supply the Virtual IP of the service

@drnybble Should i fill the announce-ip with the Virtual IP ? But how could i get the VIP before creating service?

[drnybble]

Use a bash script to perform a lookup on the hostname and then once it resovles, launch redis. Beware though that sometimes the hostname will not resolve right away you should do this in a sleep loop. Example:

# Resolve hostnames to IPs so redis doesn't get confused
if [ -n "$ANNOUNCE_IP" ]; then
  # Seems that hostname does not resolve right away so try a few times
  for i in $(seq 1 10); do
    RESOLVED_IP=$(getent hosts $ANNOUNCE_IP | awk '{print $1}')
    if [ -n "$RESOLVED_IP" ]; then
      ANNOUNCE_IP=$RESOLVED_IP
      break;
    fi  
    sleep 1
  done
fi

[martin-wong]

@drnybble Thanks for your answer. And i have another question. I have tried to run redis cluster (3 masters and 3 slaves ,as 6 service ) on docker swarm using the VIP of service and everything goes well. When i stop one node of the redis cluster , swarm will start a new instance of service automaticlly. But i still have to use the command redis-cli --cluster add-node xxx yyy in order to make the new instance joining the redis cluster .
So what's the difference between using container ip and VIP ?

[allanwax]

@martin-wong This seems like odd behavior but I'm not an docker guy, I run on bar metal. What is supposed to happen is that you set up a cluster using redis-trib and specify 3 masters and 3 slaves. They are set up to talk to each other. Upon the failure of a master the assigned slave for that master takes over.

You shouldn't have to add-node since its already there. Possibly the cluster was not set up properly. Easy check redis-cli -c -h host -p port cluster info. You should see three masters and three slaves each slave referencing the master it's a slave of. If you don't see this the cluster was not up up properly.