Connect Dockerized redis-cli to ElastiCache via AWS Bastion Host

connect-redis-cli-to-ec.sh

#!/bin/bash
# Connects a docker image of redis-cli to an ElastiCache Redis instance
# by jumping through an AWS bastion host. Setup of the bastion host is
# an exercise left to the reader, but there are many detailed explanations
# of the AWS components and security controls.
#
# NOTE:
# 1. Script assumes OSX. Tweaking required for other platforms.
# 2. Clustered Redis not supported for practical reasons.
#    Theoretically possible to establish tunnels to cluster discovery
#    host as well as all data nodes, but redis-cli doesn't support
#    connecting to multiple hosts as some clients do (redis-rb, redis-py).
#
# TODO: Set the following Bash environment variables
# 1. BASTION_HOSTNAME - AWS EC2 bastion hostname
# 2. EC_HOSTNAME - ElastiCache data node holding keys

if [ "x$BASTION_HOSTNAME" == "x" ]; then
    echo "BASTION_HOSTNAME environment variable not set"
    exit
fi
if [ "x$EC_HOSTNAME" == "x" ]; then
    echo "EC_HOSTNAME environment variable not set"
    exit
fi

REDIS_VERSION=4.0-alpine
TUNNEL_TIMEOUT=3

# See https://gist.github.com/scy/6781836 for SSH tunnel setup rationale.
ssh -f -o ExitOnForwardFailure=yes -L 127.0.0.1:6379:$EC_HOSTNAME:6379 $BASTION_HOSTNAME sleep $TUNNEL_TIMEOUT
docker run -it --rm --name redis-cli redis:$REDIS_VERSION redis-cli -c -h docker.for.mac.localhost -p 6379