问题
We're using Redis to collect events from our web application (pub/sub based) behind AWS ELB. We're looking for a solution that will allow us to scale-up and high-availability for the different servers. We do not wish to have these two servers in a Redis cluster, our plan is to monitor them using cloudwatch and switch between them if necessary.
We tried a simple test of locating two Redis server behind the ELB, telnetting the ELB DNS and see what happens using 'redis-cli monitor', but we don't see nothing. (when trying the same without the ELB it seems fine)
any suggestions?
thanks
回答1:
Placing a pair of independent redis nodes behind a LB will likely not be what you want. What will happen is ELB will try to balance connections to each instance, splitting half to one and half to another. This means that commands issued by one connection may not be seen by another. It also means no data is shared. So client a could publish a message, and client b being subscribed to the other server won't see the message.
For PUBSUB behind ELB you have a secondary problem. ELB will close an idle connection. So if you subscribe to a channel that isn't busy your ELB will close your connection. As I recall the max you can make this is 60s, meaning if you don't publish a message every single minute your clients will be disconnected.
As to how much of a problem that is depends on your client library, and frankly in my experience most don't handle it well in that they are unaware of the need to re-subscribe upon re-establishing the connection, meaning you would have to code that yourself.
That said a sentinel + redis solution would be quite ideal if your c,isn't has proper sentinel support. In this scenario. Your client asks the sentinels for the master to talk to, and on a connection failure it repeats this process. This would handle the setup you describe, without the problems of being behind an ELB.
回答2:
I came across this while looking for a similar question, but disagree with the accepted answer. Even though this is pretty old, hopefully it will help someone in the future.
It's more appropriate for your question here to use DNS failover with a Redis Replication Auto-Failover configuration. DNS failover provides groups of availability (if you need that level of scale) and the Replication group provides cache up time.
http://docs.aws.amazon.com/Route53/latest/DeveloperGuide/dns-failover-configuring.html
The Active-passive failover should provide the solution you're wanting with High Availability:
Active-passive failover: Use this failover configuration when you want a primary group of resources to be available the majority of the time and you want a secondary group of resources to be on standby in case all of the primary resources become unavailable. When responding to queries, Amazon Route 53 includes only the healthy primary resources. If all of the primary resources are unhealthy, Amazon Route 53 begins to include only the healthy secondary resources in response to DNS queries.
After you setup the DNS, then you would point that to the Elasticache Redis failover group's URL and add multiple groups for higher availability during a failover operation.
However, you might need to setup your application to write and read from different endpoints to maximize the architecture's scalability.
Sources:
http://docs.aws.amazon.com/AmazonElastiCache/latest/UserGuide/Replication.html http://docs.aws.amazon.com/AmazonElastiCache/latest/UserGuide/AutoFailover.html
回答3:
Assuming you are running in VPC:
- did you register the EC2 instances with the ELB?
- did you add the correct security group setting to the ELB (allowing inbound port 23)?
- did you add an ELB listener that maps port 23 on the ELB to port 23 on the instances?
- did you set sensible ELB health checks (e.g. TCP on port 23) so that ELB thinks the EC2 instances are healthy?
If the ELB thinks the servers behind it are not healthy then ELB will not send them any traffic.
来源：https://stackoverflow.com/questions/33125939/using-redis-behing-aws-load-balancer