Travis CI is a continuous integration service that can be used to build, test and deliver software. Travis CI is free for Free Software projects, and available for private GitHub repositories. We will use Travis CI to build your snap and push it automatically to the
edge channel of the snap store every time you make a change to your branch in GitHub.
What you’ll learn
- How to build your snap in Travis CI
- How to push your snap to the store automatically from Travis CI
- How to use snapcraft to enable all this, with a simple command
What you’ll need
- Ubuntu 16.04 or later
- A little knowledge of the Linux command line and git
- A snap store account at https://snapcraft.io/account
How will you use this tutorial?
- Only read through it
- Read it and complete the exercises
What is your current level of experience working with snaps?
What is your preferred continuous integration system?
- Travis CI
- Jenkins CI
- GitLab CI
Setting up GitHub
Before we can start the continuous delivery of snaps to the store, we will need a project with snap packaging hosted on GitHub.
If you already have your project in GitHub packaged as a snap, you can skip this step and jump straight to the next one. If you have your project in GitHub but haven’t packaged it yet, we have many tutorials that can help you making your snap. The “Create your first snap” tutorial is a good place to start.
Let’s set up one GitHub project here, in case you don’t have one ready.
First, go to https://github.com and sign up. Then, go to https://github.com/new where we will fill in the details of our new repository. The only required field is the repository name where you can enter something like
hello-snap-yourusername. That might look something like this:
Next, click the “Create repository” button to get an empty repository in GitHub. Let’s put our snap project in there!
The next step, is adding a
snapcraft.yaml file to define your snap package. To do this locally, open a terminal, and run the following commands.
The first one is to install git:
sudo apt install git
Now, clone your repository to your local workspace, using the address displayed in GitHub. Something like this, but with your username:
mkdir -p ~/workspace cd workspace git clone https://github.com/elopio/hello-snap-username.git cd hello-snap-username
To create a snap project, open a text editor, and write the following content:
name: hello-yourname version: '2.10' summary: GNU Hello, the "hello world" snap description: GNU hello prints a friendly greeting. grade: stable confinement: strict base: core18 apps: hello: command: bin/hello parts: gnu-hello: source: http://ftp.gnu.org/gnu/hello/hello-2.10.tar.gz plugin: autotools
Save it to
~/workspace/hello-snap-username/snap/snapcraft.yaml (remember to replace “username” with yours!)
This is the packaging metadata of a very simple snap, that, as the description says, will just print a greeting. The “Create your first snap” tutorial can provide details for all the lines of this file, so please refer to it to know more about the packaging. In here we will be focusing just on the continuous delivery, so let’s go on and push this snap to our GitHub repository:
git add snap/snapcraft.yaml git commit -m "add the hello snap" git push
We now have a GitHub project containing packaging details for a snap and it’s time to look at Travis CI…
Setting up Travis CI
To use Travis CI, first we will have to sign up there. Let’s go to https://travis-ci.com/auth and click “Sign in with GitHub”. Then, click “Authorize application” to allow Travis to access your GitHub account.
Now, enable the GitHub repository of your snap by clicking the “Activate repositories on GitHub” button at https://travis-ci.com/profile/, and select the repositories you want to use with Travis CI on https://github.com/apps/travis-ci
We need a
.travis.yml file for your project. Travis CI will run the steps specified in this file on every pull request and every time we make a change to any of the branches. These steps will be a few bash commands and scripts to run your tests and build your code.
First, create a file named
.travis.yml in your project folder, with the following content:
Later you can use Travis CI to run your tests. For that, you will have to adjust this file depending on the language of your project, and add the install and script steps to test and build your snap before publishing. However, we don’t need any of that yet - as we’ll just focus on continuous delivery to the store.
In the next step, we’ll make sure that your snap can be built successfully in Travis CI, so we can push the generated snap to the store.
Building the snap in a clean environment
Travis CI uses a build environment based on Ubuntu 16.04 and it has Docker support, so we will use a Docker container to build the snap.
Before we build our snap in Travis CI’s executors, we need to make sure the snap builds correctly in a Docker container.
ⓘ The need for a clean environment
When you build a snap on your machine, it could be using some dependencies that are already installed but you forgot to declare as
This means that when somebody tries to build the same snap on a different machine, those undeclared packages could be missing and the build would fail.
A clean environment, such as a default Ubuntu 16.04 or 18.04 in a container, ensures reproducible builds.
Let’s install Docker locally, to get the same environment that Travis CI will use to build the snap:
snap install docker
Go to the project directory, and run the snapcraft command in the container:
sudo docker run -v $(pwd):/my-snap snapcore/snapcraft sh -c "apt update && cd /my-snap && snapcraft"
This will take some time while Docker downloads the image, gets all the packages required by your snap, and builds it.
In the meantime, let’s take a look at the command we just ran. We are calling the
docker run command as the superuser, that’s clear. This will run a command in a docker container. The
-v argument mounts a directory in the container and the
pwd command is used to get the current directory path, this is basically giving the container access to the current directory, and mounting it in the
snapcore/snapcraft is the name of the snapcraft Docker image. What follows next is the command that we want to run in that container, so we first
cd to the mounted project directory and then run
snapcraft in there.
If everything goes well, a message like this one will be printed at the end, with the name of your snap:
If you can build your snap locally, but it fails when building it in the container, it’s likely that you are missing some
build-packages in the
snapcraft.yaml file. Use the error message to identify the missing packages, and try again until you are able to build the snap in a clean environment, without depending on your local machine.
Once you get the snap building in the Docker container, you can be confident that it will build without problems in Travis CI.
We are ready to enable continuous delivery!
Building and pushing the snap in Travis CI
The final step to enable continuous delivery from Travis CI to all your early adopters is to add some commands to the
.travis.yml file we created before. But we don’t really have to do much, snapcraft will take care of it for us.
We need to install the travis command-line utility, which will be used by snapcraft in a moment. Travis is a ruby gem, but is not available in the Ubuntu repositories, so installing it requires a few commands:
sudo apt install ruby-dev export GEM_HOME=$HOME/gems export PATH=$PATH:$GEM_HOME/bin gem install travis
To make the travis command permanently available in your path, you can add those two export lines to your
Use the command we have just installed to login to your Travis account:
travis login --com We need your GitHub login to identify you. [...] Username: elopio Password for elopio: **** Two-factor authentication code for elopio: #### Successfully logged in as elopio!
If you have yet to register your snap on the store, with your username, run:
snapcraft register hello-snap-username
Now, from the project directory, run:
snapcraft enable-ci travis
It will print a detailed explanation of what’s happening. In the previous steps we made sure to have the project configured in Travis CI, the travis command installed and the
.travis.yml file initialized. We have all the needed dependencies mentioned in the first paragraphs.
Snapcraft integration for Travis (CI). This is an *EXPERIMENTAL* feature and subject to incompatible changes in the future, please use with caution. This command currently depends on a working `travis` CLI environment and a previously initialized Travis project (`.travis.yml`). Make sure your Travis project is also configured to "Build pushes", this way every new push to `master` will result in a new snap revision in the Store. This operation will acquire properly attenuated Store credentials and encrypt them for use in your testbed (`.snapcraft/travis_snapcraft.cfg`), only Travis has the private key to decrypt it and will be only available to branches of the same repository, not forks. Then it will adjust Travis configuration ('.travis.yml') with the commands to decrypt credentials during 'after_success' phase and install latest `snapcraft` to build and release your snap (inside a snapcore:snapcraft docker container) during the 'deploy' phase. See the example below: sudo: required services: - docker after_success: - openssl aes-256-cbc -K <travis-key> -iv <travis-iv> -in .snapcraft/travis_snapcraft.cfg -out .snapcraft/snapcraft.cfg -d deploy: skip_cleanup: true provider: script script: docker run -v $(pwd):$(pwd) -t snapcore:snapcraft sh -c "apt update -qq && cd $(pwd) && snapcraft && snapcraft push *.snap --release edge" on: branch: master The dedicated credentials will be functional for exactly 1 year or until a password change on the related Ubuntu One SSO account. In order to refresh the project credentials, please run the following command: $ snapcraft enable-ci travis --refresh
Some details on what this enables:
- You will be sharing a credential with Travis CI, so you are trusting this service to properly handle the decryption key.
- The store has four channels: stable, candidate, beta and edge. Each representing an increasing level of risk. This credential works only to release your snap to edge; so there’s never risk to land a version built from a broken master in the other channels.
- The deploy step will run only after the rest of the steps declared in the
.travis.ymlfile succeed. At the moment we have no other steps, but this will be very handy after you add steps to run your unit tests. In the case that a test fails, the snap will not be deployed.
- The deploy step will run only in the master branch, so the snap will not be deployed when a branch or a pull request is created. It will only be deployed when a new commit lands in master.
- After one year, your credential will be revoked and your travis execution will start reporting an error. You will have to refresh the credential with the command:
snapcraft enable-ci travis --refresh
You can then continue the enablement:
Continue (y/N): y Enabling Travis testbeds to push and release 'hello-snap-elopio' snaps to edge channel in series '16' Acquiring specific authorization information ... Enter your Ubuntu One SSO credentials. Email: email@example.com Password: **** Second-factor auth: #### Login successful. Encrypting authorization for Travis and adjusting project to automatically decrypt and use it during "after_success". Configuring "deploy" phase to build and release the snap in the Store. Done. Now you just have to review and commit changes in your Travis project (`.travis.yml`). Also make sure you add the new `.snapcraft/travis_snapcraft.cfg` file.
Snapcraft will ask for your account information, update the
.travis.yml file, encrypt the credential in
.snapcraft/travis_snapcraft.cfg and prepare the Travis CI service to be able to decrypt that file so it can push to the store.
That’s all it took! To finish, add the two files to the git repository, commit and push, with the following commands:
git add .travis.yml .snapcraft/travis_snapcraft.cfg git commit -m 'Enable continuous delivery of the snap from Travis CI' git push
If you go to https://travis-ci.org you will see that the execution for your repository is waiting for a free slot to run, or it has already started. It will show the execution log, and if everything goes as planned, that log should end with a message like this one:
Snapped hello-snap-elopio_2.10_amd64.snap Using local configuration (`.snapcraft/snapcraft.cfg`), changes will not be persisted. Pushing 'hello-snap-elopio_2.10_amd64.snap' to the store. Using local configuration (`.snapcraft/snapcraft.cfg`), changes will not be persisted. Uploading hello-snap-elopio_2.10_amd64.snap [=============================] 100% Ready to release!| Revision 1 of 'hello-snap-elopio' created. Using local configuration (`.snapcraft/snapcraft.cfg`), changes will not be persisted. Track Arch Channel Version Revision latest amd64 stable - - candidate - - beta - - edge 2.10 1 The 'edge' channel is now open. Done. Your build exited with 0.
You should have also received an email message from Travis CI notifying you about the successful execution, and another from the store notifying you about the new snap.
Congratulations! Now you can spread the word and tell everybody to help you testing your app by running a single command:
$ snap install hello-snap-elopio --edge
Now let’s do some crowd testing!
From now on, every single change in your project will be made available to early adopters almost immediately. Your community of testers will be very happy because their edge snap will be updated automatically; they won’t have to do anything complex to help you test your most recent changes. It’s very likely that your community will grow, because they can be more involved with what’s happening in your project, they can report any issues as soon as they appear, and contribute to improve your releases. After letting this crowd testing happen for a while, you can then push to lower risk channels until you are confident enough to make it available to the world in the
Your final code directory should now have a
.travis.yml and a
.snapcraft/travis_snapcraft.cfg like the ones in this demo repository.
You can also check out the configuration CMake uses to automatically deploy new versions to the Snap Store:
You should successfully have built your snap in a clean environment, configured your project to build the snap continuously on Travis CI, and deliver a new version to the edge channel for every change on your master branch. You can relax because your delivery pipeline is all automated. Now let your community know about this, encourage them to try the edge snap, and to tell their friends how cool it is to get even more testers.
- Travis CI is very nice, but it can only build snaps for the AMD64 and Arm64 architectures. If you need to deliver your snaps for users in other architectures like armhf, you can use the snapcraft build service.
- Learn some more advanced techniques on how to use snaps by looking for other tutorials!
- Join the snapcraft.io community by subscribing to our forum.