How can I use the Chef JSON to set a redis and sidekiq configuration - redis

Question

I'm using AWS OpsWorks for a Rails application with Redis and Sidekiq and would like to do the following:
Override the maxmemory config for redis
Only run Redis & Sidekiq on a selected EC2 instance
My current JSON config only has the database.yml overrides:
{
"deploy": {
"appname": {
"database": {
"username": "user",
"password": "password",
"database": "db_production",
"host": "db.host.com",
"adapter": "mysql2"
}
}
}
}

Answer 1

Override the maxmemory config for redis
Take a look and see if your Redis cookbook of choice gives you an attribute to set that / provide custom config values. I know the main redisio one lets you set config value, as I do it on my stacks (I set the path to the on disk cache, I believe)
Only run Redis & Sidekiq on a selected EC2 instance
This part is easy: create a Layer for Redis (or Redis/Sidekiq) and add an instance to that layer.
Now, because Redis is on a different instance than your Rails server, you won't necessarily know what the IP address for your Redis server is. Especially since you'll probably want to use the internal EC2 IP address vs the public IP address for the box (using the internal address means you're already inside the default firewall).
Sooo... what you'll probably need to do is to write a custom cookbook for your app, if you haven't already. In your attributes/default.rb write some code like this:
redis_instance_details = nil
redis_stack_name = "REDIS"
redis_instance_name, redis_instance_details = node["opsworks"]["layers"][redis_stack_name]["instances"].first
redis_server_dns = "127.0.0.1"
if redis_instance_details
redis_server_dns = redis_instance_details["private_dns_name"]
end
Then later in the attributes file set your redis config to your redis_hostname (maybe using it to set:
default[:deploy][appname][:environment_variables][:REDIS_URL] = "redis://#{redis_server_dns}:#{redis_port_number}"
Hope this helps!