Logstash Redis Input connection refused - redis

Question

I'm trying to migrate a docker based redis container into AWS Elasticache. I have the Redis instance running and can connect via the redis CLI but when I setup the logstash with the following:
input {
redis {
host => "redis<domain>.cache.amazonaws.com"
data_type => "list"
key => "logstash"
codec => msgpack
}
}
It explodes with this:
[2022-02-02T13:52:27,575][INFO ][logstash.javapipeline ][main] Starting pipeline {:pipeline_id=>"main", "pipeline.workers"=>1, "pipeline.batch.size"=>125, "pipeline.batch.delay"=>50, "pipeline.max_inflight"=>125, "pipeline.sources"=>["/usr/share/logstash/logstash.conf"], :thread=>"#<Thread:0x547a32a1 run>"}
[2022-02-02T13:52:28,685][INFO ][logstash.javapipeline ][main] Pipeline Java execution initialization time {"seconds"=>1.11}
[2022-02-02T13:52:28,701][INFO ][logstash.inputs.redis ][main] Registering Redis {:identity=>"redis://#redis<domain>.cache.amazonaws.com:6379/0 list:logstash"}
[2022-02-02T13:52:28,709][INFO ][logstash.javapipeline ][main] Pipeline started {"pipeline.id"=>"main"}
[2022-02-02T13:52:28,823][INFO ][logstash.agent ] Pipelines running {:count=>1, :running_pipelines=>[:main], :non_running_pipelines=>[]}
[2022-02-02T13:52:28,837][ERROR][logstash.inputs.redis ][main][08c8cf37082e202fd617f2bc3c642b630c437b5e58521b08cd412f29ed9a10e1] Unexpected error {:message=>"invalid uri scheme ''", :exception=>ArgumentError, :backtrace=>["/usr/share/logstash/vendor/bundle/jruby/2.5.0/gems/redis-4.5.1/lib/redis/client.rb:473:in `_parse_options'", "/usr/share/logstash/vendor/bundle/jruby/2.5.0/gems/redis-4.5.1/lib/redis/client.rb:94:in `initialize'", "/usr/share/logstash/vendor/bundle/jruby/2.5.0/gems/redis-4.5.1/lib/redis.rb:65:in `initialize'", "/usr/share/logstash/vendor/bundle/jruby/2.5.0/gems/logstash-input-redis-3.7.0/lib/logstash/inputs/redis.rb:129:in `new_redis_instance'", "/usr/share/logstash/vendor/bundle/jruby/2.5.0/gems/logstash-input-redis-3.7.0/lib/logstash/inputs/redis.rb:134:in `connect'", "/usr/share/logstash/vendor/bundle/jruby/2.5.0/gems/logstash-input-redis-3.7.0/lib/logstash/inputs/redis.rb:186:in `list_runner'", "org/jruby/RubyMethod.java:131:in `call'", "/usr/share/logstash/vendor/bundle/jruby/2.5.0/gems/logstash-input-redis-3.7.0/lib/logstash/inputs/redis.rb:87:in `run'", "/usr/share/logstash/logstash-core/lib/logstash/java_pipeline.rb:409:in `inputworker'", "/usr/share/logstash/logstash-core/lib/logstash/java_pipeline.rb:400:in `block in start_input'"]}
but when I then use this configuration to provide the uri:
input {
redis {
host => "redis://redis<domain>.cache.amazonaws.com"
data_type => "list"
key => "logstash"
codec => msgpack
}
}
I get this:
[2022-02-02T13:57:10,475][INFO ][logstash.javapipeline ][main] Starting pipeline {:pipeline_id=>"main", "pipeline.workers"=>1, "pipeline.batch.size"=>125, "pipeline.batch.delay"=>50, "pipeline.max_inflight"=>125, "pipeline.sources"=>["/usr/share/logstash/logstash.conf"], :thread=>"#<Thread:0x20738737 run>"}
[2022-02-02T13:57:11,586][INFO ][logstash.javapipeline ][main] Pipeline Java execution initialization time {"seconds"=>1.11}
[2022-02-02T13:57:11,600][INFO ][logstash.inputs.redis ][main] Registering Redis {:identity=>"redis://#redis://redis<domain>.cache.amazonaws.com:6379/0 list:logstash"}
[2022-02-02T13:57:11,605][INFO ][logstash.javapipeline ][main] Pipeline started {"pipeline.id"=>"main"}
[2022-02-02T13:57:11,724][INFO ][logstash.agent ] Pipelines running {:count=>1, :running_pipelines=>[:main], :non_running_pipelines=>[]}
[2022-02-02T13:57:11,843][WARN ][logstash.inputs.redis ][main][08c8cf37082e202fd617f2bc3c642b630c437b5e58521b08cd412f29ed9a10e1] Redis connection error {:message=>"Error connecting to Redis on redis://redis<domain>.cache.amazonaws.com:6379 (SocketError)", :exception=>Redis::CannotConnectError}
The latter error looks saner but the Registering Redis line looks messed up. But neither provide any insight as to why they can't connect, yet I can connect to the Redis instance from the pod. What am I missing here?

Answer 1

Turned out on top of the config, I also had an environment variable set called REDIS_URL that was trying to gazump the config as it's used in the Redis client.
From the readme, I finally discovered:
By default, the client will try to read the REDIS_URL environment
variable and use that as URL to connect to. The above statement is
therefore equivalent to setting this environment variable and calling
Redis.new without arguments.