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How you can outline DNS in Docker containers


Jack Wallen reveals you how you can configure particular DNS servers to your Docker container deployments.

Picture: Shutterstock/roman-Samborskyi

Once you deploy a container in your community, if it can not discover a DNS server outlined in /and many others/resolv.conf, by default it’s going to tackle the DNS configured for the host machine. Which may be high-quality and dandy for sure conditions. However what if (perhaps for safety causes), you don’t want your containers utilizing the identical DNS as your hosts. Say, for instance, your host servers use a particular DNS server to stop customers from visiting specific websites. Or perhaps you will have completely different DNS configurations for VPNs.

SEE: The most effective programming languages to learn–and the worst (TechRepublic Premium)

There may be a number of causes you don’t need your containers utilizing the identical DNS as their hosts. So, what do you do? How do you outline DNS for Docker containers, such that it will not decide up the DNS of the internet hosting machine?

It is truly fairly easy. Let me present you the way.

What you may want

To make this work, you may want a machine working the Docker engine. I will be demonstrating on Ubuntu Server 20.04, however the internet hosting platform would not matter, as long as you will have Docker working and may deploy containers. You may additionally need to have a consumer that is a member of the docker group (so you are not deploying as both the basis consumer or with sudo, each of that are a safety situation). With these issues on the prepared, let’s deploy.

How you can deploy a container with DNS pre-configured

I will present you how you can deploy Docker containers with DNS pre-configured. The primary methodology will use the docker command and the second can be through Docker Compose.

As an example you need to deploy a Ubuntu container, named ubuntuDNS, with the first Cloudflare DNS server of 1.0.0.1. That command can be:

docker run -d -t --name ubuntuDNS --dns="1.0.0.1" ubuntu

You would additionally deploy that container with a main and secondary DNS like so:

docker run -d -t --name ubuntuDNS --dns="1.0.0.1" --dns="1.1.1.1" ubuntu

Let’s ensure that the container honors our DNS configuration. For that, entry the shell of the container with the command:

docker exec -it ubuntuDNS bash

From the shell, situation the command:

cat /and many others/resolv.conf

You need to see the DNS server(s) you configured from the command line (Determine A).

Determine A

dockerdnsa.jpgdockerdnsa.jpg

Our Cloudflare DNS servers have been efficiently configured.

Exit from the shell with the exit command.

Now we’ll do the identical, utilizing Docker Compose. After all, it’s a must to have this command put in, which could be carried out with the next:

wget https://github.com/docker/compose/releases/obtain/1.29.2/docker-compose-Linux-x86_64
chmod u+x docker-compose-Linux-x86_64
sudo mv docker-compose-Linux-x86_64 /usr/native/bin/docker-compose

With Docker Compose put in, now you can create the mandatory file with the command:

nano docker-compose.yaml

In that file, let’s deploy a rabbitmq (an open-source message dealer) container that may use a CloudFlare DNS entry, which is able to appear to be:

model: '3'
companies:
  service:
    dns:
      - "1.0.0.1"
           - "1.1.1.1"
    network_mode: "bridge"
    picture: rabbitmq:3-management
    container_name: rabbitmq
    hostname: rabbitmq
    ports:
      - "15672:15672"

Notice: With out the network_mode possibility set to “bridge” the DNS entry won’t work. 

Save and shut the file. Deploy the container with the command:

docker-compose up

The container will deploy. Open a brand new SSH connection to the internet hosting server (because the deployment will not return your immediate) after which entry the shell of the rabbitmq container with the command:

docker exec -it rabbitmq bash

As soon as contained in the container, view the DNS entries with the command:

cat /and many others/resolv.conf

You need to see 1.0.0.1 and 1.1.1.1 listed (Determine B).

Determine B

dockerdns-b.jpgdockerdns-b.jpg

Our WordPress deployment is utilizing the correct DNS entry.

And that is all there’s to defining DNS in your Docker containers. Why you’ll use this can rely in your wants, however having this function on the prepared could be fairly useful. 

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