{"id":953,"date":"2024-04-26T01:37:00","date_gmt":"2024-04-26T01:37:00","guid":{"rendered":"https:\/\/blog.ngocha.biz\/?p=953"},"modified":"2024-04-26T01:37:00","modified_gmt":"2024-04-26T01:37:00","slug":"keep-docker-container-running","status":"publish","type":"post","link":"https:\/\/blog.ngocha.biz\/?p=953","title":{"rendered":"How to Keep Docker Container Running for Debugging"},"content":{"rendered":"

This post will look at how to keep a Docker container<\/a> running for testing, debugging, and troubleshooting purposes.<\/p>\n

Why Does Docker Container Exit Immediately After Starting?<\/h2>\n

When you are getting started with Docker, you might face problems with Docker container exiting immediately after starting.<\/p>\n

It does not happen if you run an official Nginx container.<\/p>\n

However, if you run a base image like Ubuntu, busybox etc, or build a Docker image<\/a> without a long running process, the container will exit right after running it.<\/p>\n

The following screenshot shows both the running Nginx container and exited Ubuntu container.<\/p>\n

\"contianer<\/figure>\n

Here is why the container exit.<\/p>\n

    \n
  1. To keep the container running, you need a foreground process added to the Docker Entrypoint.<\/a> It should be a long running process.<\/li>\n
  2. In the official Nginx image, the Nginx foreground process is part of the Dockerfile Entrypoint . See official Nginx Dockerfile<\/a>.<\/li>\n
  3. Whereas, in the base Ubuntu image, there is no Entrypoint for the foreground process. That’s why it gets exited<\/strong> right after you execute the docker run command.<\/li>\n<\/ol>\n

    Let’s look at how to add an ENTRYPOINT<\/code><\/strong> to Docker that keeps the conatiner image running.<\/p>\n

    Dockerfile Command to Keep the Container Running<\/h2>\n

    Also, let’s look at another four differnt methods to keep the container running with the docker run command.<\/p>\n

    Method 1: Interactive Shell Session with pseudo-tty<\/h3>\n

    You can use the -t<\/code> (pseudo-tty) docker parameter to keep the container running. Replace tty-container <\/code><\/strong>with required name and ubuntu<\/code><\/strong> with required image.<\/p>\n

    docker run -it --name tty-container ubuntu \/bin\/bash<\/code><\/pre>\n
    Method 2: Using the tail command<\/h3>\n
    You can run the container directly by passing the tail command via CMD arguments<\/a> as shown below.<\/p>\n
     docker run -d ubuntu tail -f \/dev\/null<\/code><\/pre>\n
    Method 3:<\/strong> Using sleep infinity<\/h3>\n
    Another method is to execute a Linux sleep command to infinity. It essentially keeps the container running indefinitely.<\/p>\n
    docker run -d ubuntu sleep infinity<\/code><\/pre>\n
    Once you have the running container, you can attach the container to the terminal session using the exec<\/code> parameter shown below.<\/p>\n
    0ab99d8ab11c<\/code> is the container ID<\/p>\n
    docker exec -it 0ab99d8ab11c \/bin\/bash<\/code><\/pre>\n
    Method 4: Using Keep-Alive<\/strong> command in ENTRYPOINT<\/h3>\n
    You can also use the keep alive command like tail -f \/dev\/null<\/code><\/strong> the Dockerfile.<\/p>\n
    Here is a basic Dockerfile with an ENTRYPOINT that will keep on running without getting terminated.<\/p>\n
    FROM busybox:latest\n\nENTRYPOINT [\"tail\", \"-f\", \"\/dev\/null\"]<\/code><\/pre>\n
    The tail command follows the \/dev\/null<\/code><\/strong>, which discards all the data written to it. Due to which the tail command stays active.<\/p>\n
    Keep Container Running in Kubernetes<\/h2>\n
    Kubernetes pods<\/a> exits if you the main container running inside the pod doest have long-running process or a command that keeps the container running.<\/p>\n
    So if the default container images Entrypoint<\/a> doest have command that keeps running, the container exits immediately and the pod will go the completed state.<\/p>\n
    For example, if you run a pod with ubuntu or busybox base image, the pod will exit immediately.<\/p>\n
    Now, if you want to run a pod with image that doesnt have long running process, you will have to add custom command and arguments<\/strong> to the container specification.<\/p>\n
    Here is a Kubernetes deployment<\/a> example that uses a plain busybox image where we add a custom command sleep infinity to keep the pod running.<\/p>\n
    apiVersion: apps\/v1\nkind: Deployment\nmetadata:\n  name: test-deployment\nspec:\n  replicas: 1\n  selector:\n    matchLabels:\n      app: test-app\n  template:\n    metadata:\n      labels:\n        app: test-app\n    spec:\n      containers:\n      - name: my-container\n        image: busybox:latest\n        command: [\"sleep\", \"infinity\"]<\/code><\/pre>\n
    In summary:<\/h2>\n
    Following are the use cases where you will need a basic running container.<\/p>\n
      \n
    1. To test\/develop docker images and their configuration<\/li>\n
    2. To troubleshoot systems using utilities inside a container.<\/li>\n
    3. To troubleshoot the Kubernetes<\/a> cluster with required utilities on a pod.<\/li>\n<\/ol>\n
      We hope this article helps! If it doesn’t solve your problem or have a different use case, please drop a comment below.<\/p>\n
      If you want to learn about optimizing Docker images, check out our guide on reducing docker image size<\/a>.<\/p>\n
      \n
      Ngu\u1ed3n:<\/strong> How to Keep Docker Container Running for Debugging \u2014 DevOpsCube<\/a><\/p>\n","protected":false},"excerpt":{"rendered":"
      Source: https:\/\/devopscube.com\/keep-docker-container-running\/<\/p>\n","protected":false},"author":1,"featured_media":954,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[1],"tags":[],"class_list":["post-953","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-devops"],"_links":{"self":[{"href":"https:\/\/blog.ngocha.biz\/index.php?rest_route=\/wp\/v2\/posts\/953","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/blog.ngocha.biz\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/blog.ngocha.biz\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/blog.ngocha.biz\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/blog.ngocha.biz\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=953"}],"version-history":[{"count":0,"href":"https:\/\/blog.ngocha.biz\/index.php?rest_route=\/wp\/v2\/posts\/953\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/blog.ngocha.biz\/index.php?rest_route=\/wp\/v2\/media\/954"}],"wp:attachment":[{"href":"https:\/\/blog.ngocha.biz\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=953"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/blog.ngocha.biz\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=953"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/blog.ngocha.biz\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=953"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}