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Check How to Run Cron Inside Docker Containers
As system administrators, we are inevitably faced with the need to schedule tasks. We can achieve this using cron services on Linux systems. Additionally, we can enable cron scheduling services on container systems. In this article, we will explain the best way to enable cron services in Docker containers. Setting up a cron job inside a Docker container might not seem new to many of us. But depending on the base image we use to create the Docker image, we may face different problems.
It’s much better to run Docker cron jobs from your host system, not from within your Docker containers. Your Docker containers should have only one concern and should not be loaded with cron jobs.
How to run Cron inside Docker containers
Create a script file
- First, create a script file based on your requirements, what commands or tasks you need to run, and save it to the “.sh” file. Here, I have created a script.sh file:
Create a cron job file
- Now create a cron file and write the details of the cron job inside the file, like what time you want to run your task. Below is the sample cron file, in this the script is executed every minute.
- * * * * * echo “Test cron ran on $(date)” > /proc/1/fd/1 2>/proc/1/fd/2
Create a docker file
- Finally, create a docker file and create your docker image. Below is a sample Dockerfile.
- # Pull the ubuntu image with a specific tag from the docker hub. SINCE ubuntu: 18.04 # Add maintainer name (optional). MAINTAINER Nivesh_goyal # Update the packages and install the cron and vim editor if you later want to edit your script from within your container. RUN apt-get update && apt-get install cron -y && apt-get install vim -y# crontab file copied to cron.d directory. COPY ./files/cronjob /etc/cron.d/container_cronjob# Script file copied to container.COPY ./files/script.sh /script.sh# Grant execute permission to script file.EXECUTE chmod +x /script .sh# Execute commands to start a container.CMD
Create a dockable image
- Now run the following command to build the Dockerfile. You can change the label according to your needs:
- # docker build –tag cronjob:testing
Run the docker image inside the container.
- Now spin up a container using the image above, run the following command:
- # docker run -itd –name container_name cronjob:testing
- If you want to check if your cron is running or not, run the following command from outside the container:
- # docker logs –tail 100 -f container_name
Final remarks: How to Run Cron Inside Docker Containers
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