Logstash not connecting to Elasticsearch - using Docker-Compose

Both containers are running and are attempting to communicate with each other. I see Filebeat connecting to Logstash and send information, however I don't see any data being read into Elasticsearch.

Here are the logs that pop up when I ran the logstash container:

[2022-01-26T18:55:14,153][INFO ][logstash.licensechecker.licensereader] Elasticsearch pool URLs updated {:changes=>{:removed=>[], :added=>[http://elasticsearch:9200/]}}
[2022-01-26T18:55:14,420][WARN ][logstash.licensechecker.licensereader] Restored connection to ES instance {:url=>"http://elasticsearch:9200/"}
[2022-01-26T18:55:14,432][INFO ][logstash.licensechecker.licensereader] Elasticsearch version determined (7.16.2) {:es_version=>7}
[2022-01-26T18:55:14,434][WARN ][logstash.licensechecker.licensereader] Detected a 6.x and above cluster: the `type` event field won't be used to determine the document _type {:es_version=>7}
[2022-01-26T18:55:14,530][INFO ][logstash.monitoring.internalpipelinesource] Monitoring License OK
[2022-01-26T18:55:14,530][INFO ][logstash.monitoring.internalpipelinesource] Validated license for monitoring. Enabling monitoring pipeline.
[2022-01-26T18:55:14,642][INFO ][logstash.agent           ] Successfully started Logstash API endpoint {:port=>9600, :ssl_enabled=>false}
[2022-01-26T18:55:15,332][INFO ][org.reflections.Reflections] Reflections took 66 ms to scan 1 urls, producing 119 keys and 417 values 
[2022-01-26T18:55:16,385][WARN ][deprecation.logstash.codecs.plain] Relying on default value of `pipeline.ecs_compatibility`, which may change in a future major release of Logstash. To avoid unexpected changes when upgrading Logstash, please explicitly declare your desired ECS Compatibility mode.
[2022-01-26T18:55:16,385][WARN ][deprecation.logstash.codecs.plain] Relying on default value of `pipeline.ecs_compatibility`, which may change in a future major release of Logstash. To avoid unexpected changes when upgrading Logstash, please explicitly declare your desired ECS Compatibility mode.
[2022-01-26T18:55:16,393][WARN ][deprecation.logstash.inputs.beats] Relying on default value of `pipeline.ecs_compatibility`, which may change in a future major release of Logstash. To avoid unexpected changes when upgrading Logstash, please explicitly declare your desired ECS Compatibility mode.
[2022-01-26T18:55:16,410][WARN ][deprecation.logstash.codecs.plain] Relying on default value of `pipeline.ecs_compatibility`, which may change in a future major release of Logstash. To avoid unexpected changes when upgrading Logstash, please explicitly declare your desired ECS Compatibility mode.
[2022-01-26T18:55:16,426][WARN ][deprecation.logstash.outputs.elasticsearchmonitoring] Relying on default value of `pipeline.ecs_compatibility`, which may change in a future major release of Logstash. To avoid unexpected changes when upgrading Logstash, please explicitly declare your desired ECS Compatibility mode.
[2022-01-26T18:55:16,478][INFO ][logstash.outputs.elasticsearchmonitoring][.monitoring-logstash] New Elasticsearch output {:class=>"LogStash::Outputs::ElasticSearchMonitoring", :hosts=>["http://elasticsearch:9200"]}
[2022-01-26T18:55:16,496][INFO ][logstash.outputs.elasticsearchmonitoring][.monitoring-logstash] Elasticsearch pool URLs updated {:changes=>{:removed=>[], :added=>[http://elasticsearch:9200/]}}
[2022-01-26T18:55:16,517][WARN ][logstash.outputs.elasticsearchmonitoring][.monitoring-logstash] Restored connection to ES instance {:url=>"http://elasticsearch:9200/"}
[2022-01-26T18:55:16,522][INFO ][logstash.outputs.elasticsearchmonitoring][.monitoring-logstash] Elasticsearch version determined (7.16.2) {:es_version=>7}
[2022-01-26T18:55:16,522][WARN ][logstash.outputs.elasticsearchmonitoring][.monitoring-logstash] Detected a 6.x and above cluster: the `type` event field won't be used to determine the document _type {:es_version=>7}
[2022-01-26T18:55:16,589][WARN ][logstash.outputs.elasticsearchmonitoring][.monitoring-logstash] Configuration is data stream compliant but due backwards compatibility Logstash 7.x will not assume writing to a data-stream, default behavior will change on Logstash 8.0 (set `data_stream => true/false` to disable this warning)

For reference, here is my docker-compose.yml file:

version: '2.2' 
services:
  elasticsearch:
    image: docker.elastic.co/elasticsearch/elasticsearch:7.16.2
    container_name: elasticsearch
    environment:
      - node.name=es01
      - discovery.type=single-node
      - cluster.name=es-docker-cluster
      - bootstrap.memory_lock=true
      - "ES_JAVA_OPTS=-Xms512m -Xmx512m"
    ulimits:
      memlock:
        soft: -1
        hard: -1
    volumes:
      - ./elasticsearch/config/elasticsearch.yml:/usr/share/elasticsearch/config/elasticsearch.yml
      - data01:/usr/share/elasticsearch/data
    ports:
      - xxxx:9200
  kibana:
    image: docker.elastic.co/kibana/kibana:7.16.2
    container_name: kibana
    environment:
      ELASTICSEARCH_URL: http://elasticsearch:9200
      ELASTICSEARCH_HOSTS: '["http://elasticsearch:9200"]'
    volumes:
      - ./kibana/config/kibana.yml:/usr/share/kibana/config/kibana.yml
    ports:
      - xxxx:5601

  logstash:
    image: docker.elastic.co/logstash/logstash:7.16.2
    container_name: logstash
    environment:
      ELASTICSEARCH_URL: http://elasticsearch:9200
      ELASTICSEARCH_HOSTS: '["http://elasticsearch:9200"]'
    volumes:
      - ./logstash/config/logstashconfig.config:/usr/share/logstash/logstashC.config
    depends_on:
      - elasticsearch
    ports:
      - xxxx:5044
volumes:
  data01:
    driver: local

Can you share your logstash configuration?

From your logstash logs there is no issue for the logstash container to talk with the Elasticsearch container.

[2022-01-26T18:55:14,153][INFO ][logstash.licensechecker.licensereader] Elasticsearch pool URLs updated {:changes=>{:removed=>[], :added=>[http://elasticsearch:9200/]}}
[2022-01-26T18:55:14,420][WARN ][logstash.licensechecker.licensereader] Restored connection to ES instance {:url=>"http://elasticsearch:9200/"}
[2022-01-26T18:55:14,432][INFO ][logstash.licensechecker.licensereader] Elasticsearch version determined (7.16.2) {:es_version=>7}

Those line, and others, means that your logstash talked with your Elasticsearch without any issues.