How to Automate Docker Container Updates?

In this fast-paced software development environment, the current status of application security should be important to the DevOps team. Docker is a widely used platform for application containerization, which gives a flexible and efficient way in managing application dependencies and deployments. However, it becomes quite a challenge to keep Docker containers updated with the most recent patches, features, and security fixes if this is done manually.

This article will consider several ways to automate Docker container updates. We are going to go step by step in basic terminology, and the process of automation is attained to help one walk through with practical examples that will prove the point. You will be well versed using this guide for automating Docker container update processes to make your DevOps workflow efficient and strong.

Primary Terminologies Related to this Article

• Docker: Docker is an open-source platform for automating deployment, scaling, and management of application containers within lightweight, portable, self-sufficient containers. In other words, containers are some standalone packages incorporating literally everything an application might require to run: code, runtime, libraries, and dependencies.
• Docker Container: A Docker container is a standardized unit of software that packages up code and its dependencies so the application runs quickly and reliably from one computing environment to another. Containers are isolated from each other and bundle in everything necessary for running the application.
• Docker Image: A Docker image is a read-only template containing the environment within a Docker container. Those images are created through a series of layers, where each layer is created by the execution of a corresponding command in the Dockerfile. Images can be stored in Docker registries for distribution.
• Dockerfile: In other words, a Dockerfile is a text file that contains an ordered set of instructions used in the process of creating a Docker image. Therefore, each instruction is a layer in the image. This is the reason Dockerfiles make it possible to automate the process of creating Docker images.
• Docker Private Registry: A Docker registry is a storage and distribution system for Docker images. Public registries, such as the Docker Hub, are available for free to the public; it is also possible to set up private registries in order to maintain better control over image distribution.
• Docker Compose: Docker Compose is a tool for defining and running multi-container Docker applications. With a docker-compose.yml file, you define the application services, networks, and volumes required.
• Watchtower: Watchtower is an open-source tool that watches running Docker containers and updates them to the latest image available. As an innovative, industry-standard tool, it continuously seeks new versions of images and updates and restarts the containers accordingly.
• Cron Jobs: Cron jobs are time-based scheduled jobs in Unix-like operating systems. This enables the tool to execute scripts and commands at specific times or intervals. They become especially useful for tasks like checking new versions of Docker images.
• Rolling Updates: Rolling updates are an updating technique where old versions of software are gradually updated with new ones. Docker Swarms and Kubernetes can orchestrate the act of gradually updating old versions of software with new ones in a controlled fashion when dealing with containers.
• Orchestration Tools: Orchestration tools, such as Kubernetes and Docker Swarm, manage the deployment, scaling, and operation of application containers. This way, automated updating, scaling, and health management of containers can take place across a cluster of machines.

Step-by-Step Process for Automating Docker Container Updates

The following are the steps that helps in guiding how to automate the docker container updates:

Step 1: Launch EC2 Instance

• Go to AWS Console and login with aws credentials or create new account
• Now navigate to EC2 dashboard and launch ec2 instance

Step 2: Install docker

• We are dealing with docker so we need docker in our local machine. Install docker by using following command

sudo yum -y install docker

Step 3: Start docker daemon

• Now start and enable docker by using following command

sudo systemctl start docker
sudo systemctl enable docker
sudo systemctl status docker

Step 4: Create Docker Compose file Using Docker Restart Policies

• Docker also has restart policies in which containers can restart automatically when they exit. This is of great help, especially in ensuring the containers are running all the time, even after a system reboot or failure.

Example:

version: '3'

services:

web:

image: nginx:latest

restart: always

Explanation:

• In the above snippet of Docker Compose File, the restart: always directive makes sure that the container always starts even if it stops for whatever reason.

Using Watchtower for Automated Image Updates

• Watchtower is a well-known tool to update Docker containers automatically, running by monitoring and updating them to the latest available image version.

Installation and Usage

• Install Watchtower as a Docker container

docker run -d --name watchtower -v /var/run/docker.sock:/var/run/docker.sock containrrr/watchtower --cleanup

Explanation

• The watchtower container is started in detached mode (-d).
• -v /var/run/docker.sock:/var/run/docker.sock mounts the Docker socket into the container, allowing Watchtower to communicate with the Docker daemon.
• containrrr/watchtower is the image from Docker Hub's Watchtower.
• --cleanup removes old containers after updating.

Functionality

• Watchtower checks if there are new versions of images for running containers from time to time.
• When it identified a new image, Watchtower will pull the update and reboot the container.
• This process ensures that your containers are always up-to-date with the latest patches and features without manual intervention.

• We can check running docker container list by using following command

docker ps

• Here we see watchtower and nginx are running successfully

Using Custom Scripts with Cron Jobs

• For More advanced automation scenarios, or when Watchtower does not meet your specific needs: Write a script and use cron jobs (crontab) to periodically check for the updates of Docker images.

Example Script

• Create a shell script ( update_containers.sh ) to update Docker containers and schedule it with cron.

#!/bin/bash

# Full path to docker-compose executable

DOCKER_COMPOSE="/usr/local/bin/docker-compose"

# Pull the latest image

$DOCKER_COMPOSE pull

# Stop the running containers

$DOCKER_COMPOSE down

# Start the containers with the new image

$DOCKER_COMPOSE up -d

# Clean up old images

docker image prune -f

echo "Update completed at $(date)" >> /home/ec2-user/update_containers.log

Cron Job Setup

• Edit your cron jobs (crontab -e) so that your script is called from time to time, e.g., every night at 3 o'clock:

0 3 * * * /path/to/update_containers.sh >> /var/log/update_containers.log 2>&1

Explanation

• docker-compose pull: Pull down the latest images defined in your docker-compose.yml file.
• docker-compose up -d: Recreate containers (-d for detached mode) with new images.
• This cron job (0 3 * * *) is set to run the script every day at 3 AM, so all containers are updated without human intervention.

Here i am setting cronjobs for run the job every minute

*  *  *  *  *

• (Minutes): The job runs every minute.
• (Hours): The job runs every hour.
• (Days of the Month): The job runs every day of the month.
• (Months): The job runs every month.
• (Days of the Week): The job runs every day of the week.

* * * * * /path/to/update_containers.sh >> /var/log/update_containers.log 2>&1

Edit the Crontab

• Open the crontab editor for the ec2-user:

crontab -e

Update the Crontab Entry

• Replace the placeholder with the actual path to your script:

* * * * * export PATH=/usr/local/bin:/usr/bin:/bin:/usr/sbin:/sbin && /home/ec2-user/update_containers.sh >> /home/ec2-user/update_containers.log 2>&1

Verify the Crontab

• List the current crontab entries to verify that the cron job is set correctly:

crontab -l

Monitor the Log File

• Check the log file to verify that the script is running as expected:

tail -f /home/ec2-user/update_containers.log

• Here we see docker container was running for every minute by using this methods we can automate docker containers

Benefits of Automating Docker Container Updates

Automating Docker container updates confers several important benefits, which in turn drive efficiency, security, and reliability up the stack for your applications and infrastructure. Here are some of the most important ones:

Enhanced Security

• It automatically updates Docker containers with the latest versions, which already include security patches and fixes. This reduces the potential for vulnerabilities and protects your applications from possible security risks.

Reduced Downtime

• Updated automatically by automation tools, like Watchtower, and orchestration platforms, such as Kubernetes, a rolling update strategy replaces old container versions with new ones step by step, thus reducing downtime and ensuring that your services are available all the time.

Reliable and Reproducible Deployments

• Automate the updating process so that updates are applied evenly in all the containers and environments; this will reduce human error. Make sure your application instances are running the same up-to-date version.

Improved Efficiency

• In this way, automated updates free up many valuable work hours for the DevOps teams to engage in strategic activities, rather than the manual labor of maintenance and updates. It really boosts overall operational efficiency and productivity.

Faster Deployment of Features and Fixes

• Automated updates enable new features to be implemented and bug fixes and improvements to be introduced much faster. This agility will allow your development team to maintain the leading position through being able to respond more quickly to the needs of the customer and changes in the market.

Conclusion

An important practice in maintaining the security, stability, and performance of applications is updating Docker containers. Automating the update process of DevOps teams helps build an assurance that containers run with the latest image versions, hence reducing all the risks associated with the use of stale software and finally minimizing manual involvement.

In this article, we discussed several ways one can automate updating Docker containers. While restart policies in Docker bring basic automation—containers are restarted on failure without the need for manual intervention—Watchtower actively checks for new images and brings an update as soon as it's ready. Custom scripts with cron jobs provide maximum flexibility in this regard, as teams can set different parameters according to their needs to accomplish.

Embrace this automation practice, and in general your DevOps workflow should be more adept at keeping your applications up-to-date, secure, and performant: leading to a resilient infrastructure and more strategic work output from your team.