elasticache redis - python - connection times out

Question

I have a rather simple test app:

import redis
import os
import logging

log = logging.getLogger()
log.setLevel(logging.DEBUG)

def test_redis(event, context):
    redis_endpoint = None
    if "REDIS" in os.environ:
        redis_endpoint = os.environ["REDIS"]
        log.debug("redis: " + redis_endpoint)
    else:
        log.debug("cannot read REDIS config environment variable")
        return {
            'statusCode': 500
        }

    redis_conn = None
    try:
        redis_conn = redis.StrictRedis(host=redis_endpoint, port=6379, db=0)
        redis_conn.set("foo", "boo")
        redis_conn.get("foo")
    except:
        log.debug("failed to connect to redis")
        return {
            'statusCode': 500
        }
    finally:
        del redis_conn
        return {
            'statusCode': 200
        }

which I have deployed as a HTTP endpoint with serverless

#
# For full config options, check the docs:
#    docs.serverless.com
#

service: XXX

plugins:
  - serverless-aws-documentation
  - serverless-python-requirements
custom:
  pythonRequirements:
    dockerizePip: true



provider:
  name: aws
  stage: dev
  region: eu-central-1
  runtime: python3.6
  environment:
    # our cache
    REDIS: xx-xx-redis-001.xxx.euc1.cache.amazonaws.com



functions:
  hello:
    handler: hello/hello_world.say_hello
    events:
      - http:
          path: hello
          method: get
          # private: true # <--  Requires clients to add API keys values in the `x-api-key` header of their request
          # authorizer:   # <--  An AWS API Gateway custom authorizer function

  testRedis:
    handler: test_redis/test_redis.test_redis
    events:
      - http:
          path: test-redis
          method: get

When I trigger the endpoint via API Gateway, the lambda just times out after about 7 seconds. The environmental variable is read properly, no error message displayed. I suppose there's a problem connecting to the redis, but the tutorial are quite explicit - not sure what the problem could be.

The problem might need the need to set up a NAT, not sure how to accomplish this task with serverless

Are you able to execute the Lambda from the AWS console and have it connect to the redis then? Perhaps my answer here will assist: https://stackoverflow.com/questions/44741141/how-to-use-aws-elasticache-from-lambda-in-c-sharp — Zaxxon, Feb 07 '18 at 00:18
No, not really. I put this on the side but I am back on it. Where did you get stuck? — NoIdeaHowToFixThis, Apr 17 '18 at 11:15

feus4177 · Answer 1 · 2019-07-03T19:03:12.823

I ran into this issue as well. For me, there were a few problems that had to be ironed out

The lambda needs VPC permissions.
The ElastiCache security group needs an inbound rule from the Lambda security group that allows communication on the Redis port. I thought they could just be in the same security group.
And the real kicker: I had turned on encryption in-transit. This meant that I needed to pass redis.RedisClient(... ssl=True). The redis-py page mentions that ssl_cert_reqs needs to be set to None for use with ElastiCache, but that didn't seem to be true in my case. I did however need to pass ssl=True.

It makes sense that ssl=True needed to be set but the connection was just timing out so I went round and round trying to figure out what the problem with the permissions/VPC/SG setup was.

score 0 · Answer 2 · answered Nov 15 '18 at 07:48

0

Try having the lambda in the same VPC and security group as your elastic cluster

answered Nov 15 '18 at 07:48

Manikandan Thangavelu

21
2

elasticache redis - python - connection times out

2 Answers2