How to Properly Manage a One-Time Service Execution in Docker Swarm with Self-Deleting Containers

Описание: Discover an effective method to create a Docker Swarm service that executes just once and self-deletes without unnecessary restarts.
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How to Properly Manage a One-Time Service Execution in Docker Swarm with Self-Deleting Containers

Managing services in a Docker Swarm cluster can sometimes be tricky, especially when you want a container to perform a task once and then completely remove itself without unnecessary restarts. In this post, we'll discuss a common problem faced when setting up a service designed to run a one-time script and how to effectively solve it.

The Problem

Imagine you have a service running on your Docker Swarm cluster that needs to execute a script exactly one time and then delete itself. Unfortunately, the default behavior of Docker Swarm is to restart the container if it stops running. This means that once your script has finished executing, Swarm may automatically attempt to restart the container, leading to repeated executions.

Here's how the initial approach looks:

A service executes a script.

The container deletes itself after execution.

Swarm attempts to restart the container, causing additional unwanted executions.

The Concern

If the service takes longer than expected to execute or gets restarted within a short time frame, this can lead to problems. We want to avoid an unnecessary deletion while the job is still running.

The Solution

To ensure that your Docker Swarm service runs its script only once and deletes itself without any interruptions, you can modify the execution script and introduce a few timing adjustments. Here's the step-by-step breakdown of the solution:

Step 1: Adjust Sleep Timers

In your script that creates the temporary container, you can implement a sleep command to allow ample time for the container to complete its task before it attempts to shut down.

[[See Video to Reveal this Text or Code Snippet]]

Step 2: Introduce Waiting Mechanisms

To prevent Docker Swarm from continuously restarting the service after executing the job, you can include an additional sleep timer within the script running inside the container:

[[See Video to Reveal this Text or Code Snippet]]

Clarifying the Logic

Initial Sleep: When you first deploy your service, it waits for ten seconds. This is ample time to ensure that the container is allowed to execute its job.

Self-Deletion: After the container finishes its primary task, the sleep prevents it from stopping immediately, which provides a buffer period before Docker Swarm may attempt a restart.

Service Deletion: Once you’re finished with the execution, destroy the service programmatically, ensuring the Service does not spin up again.

Conclusion

By making these adjustments, you will create a Docker Swarm setup that effectively manages one-time service executions without worrying about unwanted restarts. The key to success lies in the strategic use of sleep commands to control timing and execution.

Now you can confidently deploy services that do the job as intended, only once. Happy containerizing!