How to Restart Docker Containers Automatically?

Restarting Docker containers automatically is very important for managing container apps. It helps to keep services running without us needing to do it by hand. This is especially helpful in production places. If we have downtime, it can cause big losses.

In this article, we will look at some key topics about automatically restarting Docker containers. We will see how we can restart Docker containers automatically. We will also talk about the different Docker restart policies and how to set them when we create containers. Also, we will learn how to change restart policies for containers we already have. We will check how to monitor Docker containers for automatic restarts. Finally, we will see how to use Docker Compose for automatic restarts. This guide will help us improve our Docker container management.

  • How Can You Automatically Restart Docker Containers?
  • What Are Docker Restart Policies?
  • How to Set Restart Policies When Creating Containers?
  • How to Update Restart Policies for Existing Containers?
  • How to Monitor Docker Containers for Automatic Restarts?
  • How to Use Docker Compose for Automatic Restarts?
  • Frequently Asked Questions

What Are Docker Restart Policies?

Docker restart policies are rules that tell how a Docker container should act when it stops. These rules help containers restart automatically based on certain conditions. This makes our applications more reliable when they run in Docker containers. Docker gives us different restart policy options:

  • No: This is the default. The container will not restart on its own.
  • Always: The container will always restart unless we stop it. This is good for containers that need to run all the time.
  • Unless-stopped: This is like “always,” but it will not restart if we stopped the container on purpose.
  • On-failure: The container will restart only if it stops with an error. We can set a maximum number of tries. For example, on-failure:5 lets it restart up to 5 times before it gives up.

We can set these policies when we create a container using the --restart flag in the docker run command:

docker run --restart=always your_image_name

To see the restart policy of a container that already exists, we can use:

docker inspect -f '{{ .HostConfig.RestartPolicy.Name }}' container_id

These policies help keep our applications running and manage how containers work in a Docker environment. For more information on controlling Docker containers, check out how to stop and start Docker containers.

How to Set Restart Policies When Creating Containers?

To make Docker containers restart automatically, we can set restart policies when we create them. We do this by using the --restart flag with the docker run command. This way, our containers can restart based on certain conditions without us having to do anything.

Restart Policy Options

Docker has some restart policies we can choose from:

  • no: This means the container will not restart automatically. This is the default option.
  • always: This means the container will always restart if it stops.
  • unless-stopped: This means it will restart unless we stop it manually.
  • on-failure[:max-retries]: This means the container will restart only if it stops with an error. We can also set a max number of times it can try to restart.

Example Command

Here is how we can set different restart policies when we create a container:

# Always restart the container
docker run --restart always -d my-image

# Restart only on failure, with a maximum of 5 retries
docker run --restart on-failure:5 -d my-image

# Restart unless stopped
docker run --restart unless-stopped -d my-image

Additional Notes

The restart policy can help keep services running in production environments.

We can check the restart policy of a running container by using this command:

docker inspect -f "{{ .HostConfig.RestartPolicy }}" container_name_or_id

By setting the restart policies right, we can make our Docker applications more strong.

How to Update Restart Policies for Existing Containers?

We can update the restart policies for existing Docker containers using the docker update command. This command helps us change the restart policy of a running or stopped container. We do not need to recreate the container.

Syntax

docker update --restart <policy> <container_name_or_id>

Restart Policy Options

  • no: It means do not restart the container automatically.
  • always: This means always restart the container if it stops.
  • unless-stopped: Restart the container unless we stop it manually.
  • on-failure: Restart the container only if it stops with a non-zero status. We can set a maximum retry count.

Examples

  1. Set the restart policy to always:

    docker update --restart always my_container

  2. Set the restart policy to on-failure with a maximum of 5 retries:

    docker update --restart on-failure:5 my_container

  3. Disable the restart policy:

    docker update --restart no my_container

Verify Changes

To check that the restart policy was updated, we can inspect the container using this command:

docker inspect -f '{{ .HostConfig.RestartPolicy.Name }}' my_container

This command shows the current restart policy for the specified container. If we want more details about the container, we can use:

docker inspect my_container

This helps us confirm that the changes are successful. For more help on managing Docker containers, we can look at how to stop and start Docker containers.

How to Monitor Docker Containers for Automatic Restarts?

To monitor Docker containers for automatic restarts, we can use some simple techniques and tools. These help us check their status and make sure they work well.

  1. Docker Logs: We can use the Docker logs command to see the output from our containers. This helps us find out if a container is restarting a lot because of errors.

    docker logs <container_id>

  2. Docker Events: We can watch Docker events to know when containers start and stop. This gives us real-time views of what is happening with the containers.

    docker events --filter 'event=start' --filter 'event=die'

  3. Docker Stats: The docker stats command helps us check the performance of running containers. This can show us problems that might cause restarts.

    docker stats

  4. Health Checks: We can set up health checks in our Docker containers. This way, they restart automatically if they become unhealthy.

    Example Dockerfile snippet:

    HEALTHCHECK CMD curl --fail http://localhost/ || exit 1

  5. Third-Party Monitoring Tools: We can use tools like Prometheus, Grafana, or Datadog. These provide deep insights and alerts when containers restart.

  6. System Resource Monitoring: We should check system resources like CPU, memory, and disk I/O where Docker runs. This tells us if resource limits cause restarts.

  7. Log Management Solutions: Using log management systems like ELK Stack can help collect logs. We can then analyze restart patterns over time.

By using these monitoring strategies, we can track Docker containers and their automatic restarts. This helps us keep our applications available and reliable.

How to Use Docker Compose for Automatic Restarts?

Docker Compose makes it easy to manage Docker containers and services. It also helps us set up automatic restarts. We can tell Docker how to restart containers in the docker-compose.yml file.

To set up automatic restarts, we use the restart key in our service definition. Here is a simple example:

version: '3.8'
services:
  my_service:
    image: my_image:latest
    restart: always
    ports:
      - "80:80"

Restart Policy Options

We can pick from different restart policies:

  • no: Do not restart the container automatically. This is the default option.
  • always: Restart the container every time it stops.
  • unless-stopped: Restart the container unless we stop it manually.
  • on-failure: Restart the container if it fails with a non-zero status. We can also set a maximum number of retry attempts:
restart: on-failure:5

Deploying with Docker Compose

Once we write our docker-compose.yml file, we can deploy our services with this command:

docker-compose up -d

This command starts our containers in detached mode. The restart policies we set will work now.

Monitoring and Updating

To check the status of our services and see if they are restarting correctly, we use:

docker-compose ps

If we want to change the restart policy for a service, we change the docker-compose.yml file. Then we redeploy with:

docker-compose up -d

By using Docker Compose for automatic restarts, we can make our applications in containers more reliable.

For more details about Docker and its features, we can look at this article on Docker container lifecycle.

Frequently Asked Questions

1. How do Docker restart policies work?

Docker restart policies help us set how Docker containers act when they stop. We can choose policies like always, unless-stopped, or on-failure. This way, our containers restart by themselves under certain situations. This feature is very important for keeping our applications running and making them more reliable.

2. Can I change the restart policy of a running Docker container?

Yes, we can change the restart policy of a Docker container that is already running by using the docker update command. For example, to make a container restart always, we can write:

docker update --restart always <container_name>

This helps us change how our container works without having to create it again. It makes managing easier.

3. What is the default restart policy for Docker containers?

By default, Docker containers do not have a restart policy. This means they will not restart automatically when they stop. If we want our containers to restart by themselves, we have to set a restart policy when we create the container using the --restart flag.

4. How can I monitor Docker containers for automatic restarts?

We can monitor Docker containers with the docker ps command. This lets us check their status. We can also use the docker logs command to see the logs. There are tools like Prometheus or Grafana that can give us more details about container restarts and health. This helps us watch performance and solve problems better.

5. Is it possible to use Docker Compose for automatic restarts?

Yes, Docker Compose lets us set restart policies for our services right in the docker-compose.yml file. We can say the restart policy for each service under the deploy section. This makes it easy to control container behavior in a setup with many containers. For example:

services:
  myservice:
    image: myimage
    restart: always

This makes sure our services restart automatically when needed.

For more insights into Docker’s function, check out What is Docker and Why Should You Use It? or learn about Docker Container Lifecycle to understand better how to manage your Docker containers.