Question 121138 in Redis Question posted in
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Hosting Redis on EC2 – ConnectionTimeoutError

I have an EC2 instance behind a load balancer. The security group attached to it allows for inbound connections (both ipv4 and ipv6 on port 6379). I am able to connect to my redis client:

redis-cli -h ec2-**-**-**-*.us-west-1.compute.amazonaws.com -p 6379

However, when I try to connect with nodeJS and express-session I get a ConnectionTimeoutError on EC2, but locally it works fine:

const redisClient = createClient() // uses default port localhost:6379 
redisClient.connect().catch(console.error)

If there is a race condition here, like others mentioned, why does this race condition happen on EC2 and not locally? Is the default localhost incorrect since there is a load balancer in front of the instance?

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Answers


  1. Chosen as BEST ANSWER
    0

    Redis client should be instantiated explicitly in a setup like this one (covers both ipv4 and ipv6 inbound traffic):

    createClient({ socket: { host: '127.0.0.1', port: 6379 }, legacyMode: true })

    As redis is self-hosted on EC2 with a load balancer in front of the instance, localhost may not be mapped to 127.0.0.1 as a loopback address. This means that the default createClient() without a host or port specified, might try to establish a connection to a different internal, loopback address.

    (Make sure to all inbound traffic to tcp 6379, or the port you are using)


  2. 0

    Based on your comments, I’d say the problem is the load balancer. Redis communicates on a protocol based on TCP. An ALB is only for HTTP/HTTPS traffic, so it cannot handle this protocol. Use a Network Load Balancer instead, with a TCP listener. Also make sure your security group rule also allows TCP traffic for port 6379.

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