ElasticSearch + LogStash + docker-compose: simple logstash.conf without volume mount - docker

Question

Small question regarding ElasticSearch + LogStash + docker-compose, and the possibility to start LogStash with a configuration logstash.conf without volume mount please.
For testing purpose, I would like to start an ElasticSearch and a LogStash. The LogStash purpose is to forward logs to the ElasticSearch cluster.
Popular logstash.conf found on the web are like this:
input {
tcp {
port => 5000
codec => json
}
}
output {
elasticsearch {
hosts => ["http://elasticsearch.mynetwork:9200"]
index => "myapp"
}
}
If I save this as a file, and mount it in my dockerfile, it works like a charm, very happy.
However, it requires to mount a file from the local system onto the container.
Since this configuration file is super simple, I was wondering if I could just pass the content of the config file as environment variable in the docker compose file.
Here is what I tried:
version: "3.9"
services:
elasticsearch:
networks: ["mynetwork"]
container_name: elasticsearch.mynetwork
hostname: elasticsearch.mynetwork
image: elasticsearch:8.6.0
ports:
- 9200:9200
environment:
- discovery.type=single-node
- xpack.security.enabled=false
ulimits:
memlock:
soft: -1
hard: -1
logstash:
networks: [ "mynetwork" ]
container_name: logstash.mynetwork
hostname: logstash.mynetwork
image: logstash:8.6.0
ports:
- 9600:9600
- 5044:5044
- 5000:5000/tcp
- 5000:5000/udp
environment:
LS_SETTINGS_DIR: input { tcp { port => 5000 codec => json }}output { elasticsearch { hosts => ["http://elasticsearch.mynetwork:9200"] index => "myapp" }}
However, LogStash is not able to forward to Elastic.
May I ask what is the proper way to configure LogStash, so that it can take into account the conf file without mounting it as a volume please?
Thank you