Six things to monitor in a Docker Compose stack
You have deployed your stack with Docker Compose. Your containers are running. Everything seems to be working. But what happens when something breaks at 3 AM? This checklist covers the six things worth monitoring in a Compose stack, whatever tool you use to do it. 1. Containers The most basic level: are your containers running? Container state : running, stopped, restarting, exited Restart loops…
When utilizing Docker Compose, it's crucial to monitor several key aspects to ensure the smooth operation of your stack, even when issues arise during off-hours. Here are six essential points to monitor:
1. Containers: Begin by verifying whether your containers are functioning correctly. Check their state - are they running, stopped, restarting, or exited? Be aware of restart loops, which can be more problematic than a container that has merely stopped. Utilize Docker health checks, which are often underused but highly beneficial. Monitor exit codes, as a non-zero exit code indicates a crash rather than a clean shutdown. Include a health check within your docker-compose.yml file to set up a proper monitoring system.
2. Endpoints: Verify that your services respond appropriately to requests. Conduct HTTP checks to ensure that the status code and response time meet your expectations. Additionally, perform SSL certificate validation to ensure that certificates are valid and not expired. Some services, such as databases, Redis, or MQTT, may not use HTTP. In such cases, TCP checks can be employed to confirm that the port is open and accepting connections.
3. SSL Certificates: Expired SSL certificates can lead to preventable downtime. Although Let's Encrypt and automatic renewal processes may seem sufficient, renewals can fail without any warning signs. To mitigate this risk, set alerts well in advance of certificate expiration (e.g., at 30, 14, 7, 3, and 1 day) so that you can address any failed renewals promptly.
4. Cron Jobs: Scheduled tasks, such as backup and cleanup jobs, are often overlooked but critical components of your stack. To ensure these tasks are running correctly, implement the heartbeat pattern. Have each job send a ping to a designated URL after completing its execution, and configure your monitoring system to alert you if the ping does not arrive within the expected timeframe. Additionally, report the exit code and send the ping regardless of whether the job succeeded or failed.
5. System Resources: Keep an eye on your system resources, including disk space, memory usage, CPU, and network I/O. A full disk can cause your database to crash, while high memory usage and abnormal CPU spikes can indicate potential issues. Network congestion can also lead to problems, so monitor this metric as well. Set appropriate thresholds for each resource, allowing for some margin, and maintain historical data to distinguish between a temporary spike and a persistent trend.
Utilize the Docker stats API to gather per-container information related to CPU, memory, network, and block I/O.
6. Image Updates: Staying informed about available security updates for your images is essential. By comparing the digest of the image you are running with the one available in the registry, you can identify when newer builds exist for the tag you are using. This proactive approach helps ensure that your stack remains secure and up-to-date.
Written by urgent.news from Dev.to's reporting — not their text. Machine-written — may contain errors; check the original before relying on it.
