Installing Docker and Docker Compose on Linode
September 3, 2017

This is the second post in a series of blog posts about how to run an experiment with Amazon Mechanical Turk, using psiTurk.

This post will cover how to install Docker and Docker Compose, which we will use to run the two programs necessary for deploying an experiment with psiTurk: MySQL and psiTurk itself.

This picks up from the previous post, where we configured a virtual private server on Linode.

What is Docker and why use it?

Docker is a software container platform. What this means is that Docker allows you to run programs inside of containers that are isolated from the host computer. Docker allows you to specify how exactly to build the container, which helps ensure that the program you want to run inside of the container has access to everything it needs.

This is useful for several reasons. For example, it ensures that the program runs exactly the same way on two completely different computers; it also allows you to automate the creation of a new development or production environment. (For more information, head over to Docker’s website.)

There’s also a Docker tool called Docker Compose, which allows you to run multiple containers on the same host machine in an automated and coordinated manner. Using Docker Compose will thus allow for deploying both a database and psiTurk itself on the Linode server that you’ve set up.

The application stack: MySQL and psiTurk

As you may know, with psiTurk it is necessary to hook your experiment up to a database so that you can record the data from participants as they participate. By default, psiTurk is configured to use SQLite, which is not the most robust database. Particularly, it is a bad idea to use SQLite when you actually deploy your experiment to Amazon Mechanical Turk. SQLite won’t do well if multiple people are doing the experiment at the same time; you might lose data. Instead, you want to use MySQL, which is a more robust database.

In addition to running MySQL, you’ll also need to run psiTurk itself. Creating a Docker container for each of these programs will be covered later in the series. This post focuses on installing docker and docker-compose.

Installing Docker

If you’re not already logged in to your Linode account that you set up in the previous post, go ahead and log in to it using SSH (again, replace the 0’s with your server’s IP address and your_username with your username):

ssh your_username@00.000.000.00

Next, you can install Docker by curl-ing and running a script that the Docker folks maintain for installations:

curl -sSL https://get.docker.com/ | sh

At the end, you’ll probably see a message suggesting that you add yourself to the newly created docker group. Doing so would allow you to run docker commands without having to use sudo. If you do decide to do this, you can add yourself to the docker group by running the following command (replacing your_username with your username):

sudo usermod -aG docker your_username

In order for this to take effect, you’ll need to log out and log back in.

Next, you’ll need to install Docker Compose. This is done by curl-ing a file from GitHub and saving it to your server, after which you’ll need to give it executable permissions. You’ll want to download the latest version of Docker Compose, which you can find by following this link. After you follow that link, you should see some commands to execute. At the time of writing, the most recent version of Docker Compose is 1.15.0, so the first command to run is:

sudo bash -c "curl -L https://github.com/docker/compose/releases/download/1.15.0/docker-compose-`uname -s`-`uname -m` > /usr/local/bin/docker-compose"

If you’re reading this in the future, the command will likely be slightly different in order to reflect the most recent version. You’ll have to change the version number after /download/ in the URL. Moreover, note that the command above is slightly different than what is suggested on the GitHub release page. There, they just suggest the part of the command which is in quotes above. However, since the results of the curl are being redirected to the file /usr/local/bin/docker-compose, you’ll need root permissions in order to save the file because /usr/local/bin is a directory that is owned by root. This isn’t quite as simple as just running sudo curl ... > /usr/local/bin/docker-comopose because that only executes the curl command as root. It doesn’t do the redirecting (>) as root. To get the redirect to happen with root permissions, you’ll need to run sudo bash -c "COMMAND HERE", replacing COMMAND HERE with the redirected curl command.

And just to note one last time: if you’re reading this in the future, you will again want to follow this link in order to get the latest version.

Next, after curl-ing the file, you’ll need to make it executable with the following command:

sudo chmod +x /usr/local/bin/docker-compose

Now you should be able to run the docker-compose command. Congrats!

In the next post in the series, you’ll learn how to set up the psiTurk Docker container.

Please feel free to comment with any questions! And, if you are finding this information helpful, please consider signing up for Linode using my referral link. Thanks! 🙇