Category Archives: Docker

Hosting a github like service on my Ubuntu server

I was thinking it would be cool to host some private git repositories on my Ubuntu server. That’s where Gogs comes in.

Sure I could have created a git repository “manually” but why bother when Gogs comes in a docker instance as well (and I love Docker).

Excellent documentation is available on the Gogs website or via Docker for Gogs on GitHub. But I will be recreating the bare essentials here so I know what worked for me.

First off, we’re going to need to create a Docker volume. For those unfamiliar with Docker, data is stored in the instance of Docker and therefore lost when it shuts down. To allow data to persist beyond the life of the Docker instance, we create a Docker volume.

So first up, I just used the default Docker volume location using

docker volume create --name gogs-data

On my Ubuntu installation, this folder is created within /var/lib/docker.

Next up we’ll simply run 

docker run --name=gogs -p 10022:22 -p 10080:3000 -v gogs-data:/data gogs/gogs

This command will download/install an instance of gogs and it will be available on port 10080 of the server. The instance will connect it’s data through to our previously created volume using the -v switch.

From your chosen web browser, you can display the Gogs configuration web page using http://your-server:10080.

As I didn’t have MySQL or PostgresSQL set-up at the time of installation, I simply chose SQLite from the database options shown on the configuration page.

That’s pretty much it – you’ll need to create a user login for your account and then you can start creating repositories.

I’m not sure if I’m doing something wrong, but I noticed that when you want to clone a repository, Gogs says I should clone

http://localhost:3000/mark/MyApp.git

Obviously localhost is no use from a remote machine and also 3000 seems to be incorrect, and should be 10080 (as specified in the run command).

lookup index.docker.io no DNS servers error

I’ve been learning Docker lately and all was working well, then today I started seeing the following error lookup index.docker.io no DNS servers error when trying to pull a docker container from Docker Hub. Very strange as this worked fine previously.

For the record, I was able to use apt-get to update packages and I could ping the index.docker.io address, so I’m not sure what changed to make this break.

Anyway to solve the problem we can simply append dns-nameservers to the file /etc/network/interfaces

For example

auto lo
iface lo inet loopback

auto eth0
iface eth0 inet static
address 192.x.x.x
netmask 255.255.255.0
gateway 192.x.x.1
dns-nameservers 8.8.8.8 8.8.4.4

In the above I’ve added the loopback and two google name servers to the interfaces file.

To activate these changes (without a reboot) just use

ifdown eth0 && ifup eth0

Getting started with Docker

I’ve been wanting to try out Docker for a while. Finally got my Ubuntu 14.04 server up and running, so now’s the time.

First off I installed docker as per the instruction on How to Install Docker on Ubuntu 14.04 LTS.

What version of Docker am I running?

Simple enough, just type docker version. Assuming the docker daemon is running you should see various bits of version information.

I’m currently running Client version 1.0.1

How to search for container images

We’re going to start by simply trying to find an existing images that we can pull onto our server, so typing docker search <name of image> will result in a list of images found with a match on the supplied image name.

For example docker search mongodb will return a list from the Docker hub of images with mongodbInstalling an image

Once we’ve found the image we want we need to “pull” it onto our machine using docker pull <name of image>

So let’s pull down the official mongodb image

docker pull mongo

This command will cause docker to download the current mongo image. Once completed you will not need to pull the image again it will be stored locally.

Hold on where are images stored locally?

Run docker info to see where the root directory for docker is, as well as information on the number of images and containers stored locally.

Runnning a container

Once we’ve pulled down an image we can run and application within the container, for example docker run <name of image> <command to run>

Let’s run our mongodb container by typing the following

  • docker run –name some-mongo -d mongo
  • docker run -it –link some-mongo:mongo –rm mongo sh -c ‘exec mongo “$MONGO_PORT_27017_TCP_ADDR:$MONGO_PORT_27017_TCP_PORT”‘

In the above some-mongo should be replaced with the name you want to use.

Note: These command lines will run mongodb in interactive mode, i.e. we will be placed into the mongodb shell.

Updating the container

An image itself may be based upon an OS, such as Ubuntu. So we can actually run commands on the operating system in the container, for example apt-get. Installing software into an OS container is cool but we will then want to persist such changes to the container.

Whilst the changes have been made, they are not yet persisted to the containter. To persist our changes we need to commit them.

First we need to find the ID of the container, for example running docker ps -l, then we save the changes using docker commit <ID> <new container name>.

You needn’t type the whole ID from the call to docker ps -l, the first three or four characters (assuming they’re unique) will suffice.

The value returned from the commit is the new image id.

Inspect

We can view more extensive information on a container by using docker inspect <ID>. Remember the ID can be found using docker ps.

Inspect allows is to see all sorts of information including the image’s IP address.

Pushing an image to the Docker Hub Registry

Once we’re happy with our image we can push it to the docker hub to allow others to share it. Simply use docker push <name of image>.

To find the images on your machine simply use docker images.

Removing all containers and all images

We can use docker’s ps command along with the docker rm command

docker rm $(docker ps -a -q)

to remove all containers and we can use the docker rmi command to remove images as follows

docker rmi $(docker images -q)