RedisException: MOVED 3889 / AWS MemoryDB

That sounds like you’re using a real Redis Cluster (cluster_enabled).

The WP_REDIS_HOST won’t work, because Redis Object Cache needs to know all primary cluster nodes. Instead use:

define( 'WP_REDIS_CLUSTER', [
    'tcp://127.0.0.1:6379?alias=primary-01',
    'tcp://127.0.0.2:6379?alias=primary-02',
    'tcp://127.0.0.3:6379?alias=primary-03',
] );

Whether you have multiple or a single primary node, you must use the WP_REDIS_CLUSTER configuration, instead of WP_REDIS_HOST.

Hi @tillkruess
thank you very much for your fast response. I’m aware of that this is no standard and we’re grateful for that.

Well actually we tried this as well. None of the configurations we tried is working. Once switching to WP_REDIS_CLUSTER, we’re getting as error:

epoll_wait() reported that client prematurely closed connection, so upstream connection is closed too while reading upstream

We need to connect via tls, with user and password. Logging in into each of our nodes from the WordPress container via redis-cli works fine:

redis-cli -h xxx-0001-001.xxx.xxx.memorydb.sa-east-1.amazonaws.com --user $REDIS_USER --pass $REDIS_PASSWORD --tls

As said, the connection via WP_REDIS_HOST with the following URL once worked (so I can assume that in general all the required data arrives at the php code:

clustercfg.xxx.xxx.memorydb.sa-east-1.amazonaws.com

So I’m wondering why this leads to a connection close:

define( 'WP_REDIS_CLUSTER', [
    'tcp://xxx-0001-001.xxx.xxx.memorydb.sa-east-1.amazonaws.com:6379',
    'tcp://xxx-0001-002.xxx.xxx.memorydb.sa-east-1.amazonaws.com:6379',
    'tcp://xxx-0002-001.xxx.xxx.memorydb.sa-east-1.amazonaws.com:6379',
    'tcp://xxx-0002-002.xxx.xxx.memorydb.sa-east-1.amazonaws.com:6379',
] );

Also tried the protocols redis, rediss and tls.

Any idea how to continue from here?

Of course the epoll_wait error is comming from nginx. The fpm does simply time out.

To exclude the option that the epoll_wait timeout is due to missing memory or cpu, we removed the container limits temporarily for the container. Also we raised the fpm pm values:

pm.max_children = 25
pm.start_servers = 5
pm.min_spare_servers = 5
pm.max_spare_servers = 10
pm.max_requests = 500

Should be sufficient enough…

• This reply was modified 1 year, 3 months ago by shvayapin.

I’d suggest making a redis.php file on your EC2 instance and trying to connect manually via PhpRedis, once you figured out which configuration allow you to connect to your Elasticache Cluster, then I can tell you which WP_REDIS_* constants to use.

Using WP_REDIS_HOST will not work, because MOVED responses aren’t handled.

You may also try using Predis, maybe that works better?

You can bypass the Nginx issues by using php CLI first.

I know that people use Elasticache Clusters with Redis Object Cache, these forums may have some code snippets.