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Is it possible to connect from an AWS Lambda function to a Redis ElastiCache cluster?
I can't figure out if it's a configuration problem or it's simply not possible.
PS: I made a test from an EC2 instance and I can connect to the Redis node. Also the Lambda function and the Redis node are in the same region.
UPDATE (09 Oct 2015):
Amazon announced VPC for AWS Lambda functions. Details here
This means we can now access any resource in AWS behind VPC security group, including ElastiCache and RDS machines.
UPDATE (11 Feb 2016): Amazon launched VPC for AWS Lambda.
As of Feb 2016, AWS allows using lambda functions to connect to Elasticache. Refer to Access Resources within a VPC using AWS Lambda. Here is a link how it works - Tutorial: Configuring a Lambda Function to Access Amazon ElastiCache in an Amazon VPC
Setting up an HTTP Proxy or iptables wouldn't work for the following reasons:
Redis calls are not
HTTP and will not be handled by HTTP proxies.
iptables (or any port forwarding for that matter) will either won't accept a domain name as destination or is highly inefficient due to DNS resolution required every time.
The best and convenient method is to install
twemproxy in an EC2 machine and route your requests through it. As a bonus, you suddenly have deployed a fantastic sharding strategy as well.
I was experiencing the same issue. I did not find a direct solution but instead used a Lambda function to connect to an EC2 server using socket.io which was pretty easy and emit an event to that EC2 server.
When the EC2 server received the event it performed the necessary Redis task ( database cleanup after image thumbnail generation ).
Hope this helps! If anyone finds out how to connect to ElastiCache from Lambda directly I'd still love to know!
I have tried connecting lambda to memcached elasticache and it works fine. Redis should also be doable.
Couple of things to keep in mind:
You can use (Redislabs) managed cloud solution which can be connected without VPC.
There will be no VPC cold starts with cloud solution, but there will be a latency overhead because the call to managed redis is made over internet. The additional latency is around 20 ms when lambda and redis are deployed in the same region. This is manageable for my use case and I don't need to worry about VPC.