How can you view logs in an already running container?

The simplest way to use the docker logs command.

# View all logs of a container
docker logs <container_id_or_name>

# View only the last N lines of logs
docker logs --tail N <container_id_or_name>

# View logs since N (in Unix timestamp format)
docker logs --since N <container_id_or_name>

# Follow new logs in real-time
docker logs -f <container_id_or_name>

# View logs with timestamps
docker logs -t <container_id_or_name>

# Combining options
docker logs -tf --tail 100 <container_id_or_name>

If more in-depth analysis is required or there are specific requirements for log storage and aggregation, specialized tools can be used:

• Fluentd/Logstash/Filebeat: Collect logs from containers and send them to a centralized storage.
• Elasticsearch/Splunk/Loki: Systems for indexing, storing, and searching logs.
• Kibana/Grafana: Tools for visualizing logs and creating dashboards.

The choice of method depends on the infrastructure and needs. For quick "debugging" viewing, docker logs is usually sufficient. In production environments, a centralized logging system is almost always required.