redis-cli connection to Amazon ElastiCache Redis cluster hangs up

Question

I have installed and compiled Redis from source and am attempting to connect to an Amazon ElastiCache (Redis) cluster.

I can connect to the default localhost with no problem, but attempting to connect to an AWS endpoint causes what seems to be an infinite hangup.

With defaults:

$ redis-server /etc/redis.conf  # daemonized, uses localhost
$ redis-cli ping
PONG
$ sudo service redis_6379 status
Redis is running (12919)
$ redis-cli shutdown  # or sudo service redis_6379 stop

Now, here is an attempt to connect to the endpoint, copies from AWS documentation on the topic:

redis-cli -c -h my_example_endpoint_name.eaogs8.ng.0001.use1.cache.amazonaws.com -p 6379 ping

This hangs up infinitely without anything being issued to stderr/stdout.

(Please note this is an example endpoint name; I have verified I am using the primary endpoint listed at the AWS console.)

I suspect this may be related to the security group settings for the cluster on the AWS side but am not sure specifically what could/should be modified. I appreciate suggestions of what could be blocking the connection and can provide info on the cluster itself as needed.

Answer 1

The connection was being prohibited by the security groups of the EC2 instance and the ElastiCache cluster to which it was trying to connect not being properly aligned.

From the AWS docs:

All ElastiCache clusters are designed to be accessed from an Amazon EC2 instance. The most common scenario is to access an ElastiCache cluster from an Amazon EC2 instance in the same Amazon Virtual Private Cloud (Amazon VPC).

The steps that I took to correct this were:

1. Navigate to the ElastiCache Dashboard > Redis and click on the Cluster Name in question. This will show a Security Group field where the value is a Group ID such as sg-x8xxxxxx.
2. Navigate to your Security Groups table under https://console.aws.amazon.com/ec2 > Network & Security > Security Groups. Find the Group ID from step 1 and note its corresponding Group Name.
3. Navigate to your EC2 Management Console at https://console.aws.amazon.com/ec2 > Instances > Instances. For the server you are using to try to connect to the Redis cluster, take note of the Security Groups field. This must include whatever the Group Name was from step 2. If it doesn't, you need to add this security group. Check the box next to the server name, Actions > Networking > Change Security Groups. Add the security Group Name so that the two components share the same VPC.

You should now be able to connect with something like (example):

redis-cli -c -h mycachecluster.eaogs8.0001.usw2.cache.amazonaws.com -p 6379 ping