Rootstrap Blog

How to Automate iOS & Android App Builds Using Fastlane & GitHub

Mobile app development is one of our core competencies here at Rootstrap, and we embrace best practices for development and delivery just as much as we do for backend and web applications.

As Continuous Integration/Continuous Delivery requires maintaining multiple backend environments (Development, QA, Staging, Production), with fully automated deployments to each, it also requires maintaining multiple versions of our mobile apps to match each environment.

Building and releasing all these versions is a time-consuming and error-prone process, which can -and should- be automated, though it presents a particular set of challenges.

In this post I am going to describe the approach we implemented for iOS and Android CI/CD making use of Fastlane, a CI system (GitHub Actions), and some spare Mac Minis which were sitting idle at the office and got turned into build servers.

We’ll use AWS S3 to store signing artifacts, but any system where we could safely store encrypted files could serve.

For the first example, we will use an iOS app developed with React Native, but the same approach works iOS native apps.

Why Fastlane

Fastlane touts itself as the easiest way to automate deployments for mobile apps. It offers integrations with other CLI tools and APIs including Xcode, Android SDK, Gradle, iTunes App Store, Google Play Store, Git, AWS S3, etc. We adopted it because we found it to be:

  • Easy to set up (just install a Ruby gem)
  • Flexible, with an easy to read syntax (most commands have self-descriptive aliases)
  • Open Source and free to use
  • Widely adopted and well maintained (acquired by Google in 2017)
  • Easy to integrate with CI systems (though 2FA presents challenges, as we’ll see)

Why GitHub Actions

GitHub offers Actions as a complete CI/CD system that seamlessly integrates with repositories hosted there. Our experience showed it to be:

  • Easy to write and read, with a straightforward YAML syntax
  • Flexible, offering hosted runners in every major OS and integrations with pretty much every major tech stack and hosting platform
  • Cheap -considering it is free for Open Source projects and when using self-hosted runners (this is where our spare Mac Minis become valuable)

Prep Work

Application Targets

Within our Xcode project, we would define multiple iOS build targets with build settings corresponding to each target environment. Each of these will need to be associated to an app bundle ID created in the Developer Portal, and listed in the AppStore Connect site.

We should disable Xcode automatic signing for the targets we want to handle with Fastlane and associate the corresponding Provisioning Profile. This configuration should be checked into our repo to be picked by the CI system (we can always override them to use automatic signing locally).

Code Signing

We know that for an iOS app to be distributed, it needs to be signed with a certificate issued by Apple, and a provisioning profile allowing you to install or distribute the application with this certificate. So, after registering these apps we will need:

We can store the password for the .p12 file in GitHub Secrets and make it available to the workflow as an environment variable when importing it.

All three files should be uploaded to a secure location that our CI process will have access to. Fastlane suggests using match for this, which is a pretty good solution but has some limitations:

  • It only works for iOS
  • It cannot be extended to cover other sensitive files a build might need
  • It requires access to a specific GitHub repo for each project, which involves some extra steps when running from a CI/CD server

So, the solution we are trying here makes use of Amazon S3. This works well for us as we typically use S3 in all our projects (Frontend and Backend), and normally have AWS credentials in our working environment.

One single private bucket, encrypted with AWS KMS, allows us to securely handle our Certificates, Keystores, and other sensitive files for all our projects. It is a good practice to create a specific user for our CI workflow which only has access to the proper bucket and path. You can read about Access Management for S3 here

Our workflow thus only needs to include environment variables with valid AWS keys, which should be also stored as repo Secrets.

  • AWS_ACCESS_KEY_ID
  • AWS_SECRET_ACCESS_KEY

Apple ID

In order to authenticate to App Store, Connect Fastlane recommends using a dedicated Apple ID that doesn’t have 2FA enable and is not an Account Holder. However, it is currently not possible to create a new Apple ID without 2FA (and old accounts cannot remove it once enabled).

This means when it needs to authenticate to the App Store from a new machine, Fastlane will prompt for a security code which will be sent to a trusted device. There are two possible workarounds for this when running on CI systems, both with significant limitations:

  • Generating a temporary Apple login session and storing it in the FASTLANE_SESSION variable. This can be done using Fastlane’s spaceauth feature. It is however restricted not only in duration (one month) but also geographically (cannot be used in a different region from where it is generated).
  • Apple application-specific passwords can be generated on the Apple ID site. These are made available to Fastlane through the environment variable FASTLANE_APPLE_APPLICATION_SPECIFIC_PASSWORD. However, these are only good for uploading binaries to TestFlight, so in order to add the information required by the App Store for a release Fastlane stills needs to authenticate, otherwise, the build gets uploaded but it is not usable.

For use of our CI workflow, in addition to the latter option, we will manually log into our build servers with our shared Apple ID, associating them as trusted devices.

The following environment variables will need to be present in our workflow, so we should store their values as repo Secrets:

  • FASTLANE_USER : Apple ID used for submission
  • FASTLANE_PASSWORD : Password for this ID
  • FASTLANE_APPLE_APPLICATION_SPECIFIC_PASSWORD: Application-specific password
  • FASTLANE_ITC_TEAM_ID : iTunes Connect Team ID to submit under

See Fastlane docs on Apple Authentication for more info and options.

Other Environment Variables & Files

For a React Native project, we would typically have a .env file with multiple environment-specific variables, including but not limited to the backend URL that each version of our app should target.

Likewise, for an iOS-native project, we could have .xcconfig files including environment-specific params, several of which could be sensitive.

There are several ways to securely handle and process these items, but in this example, we will store all the relevant parameters as repo Secrets and read them as environment variables in our workflow, in order to build this .env file at runtime.

So, for instance, our DEV workflow would have an API_URL environment variable pointed to the DEV_API_URL repo Secret.

The Fastfile

Environment Settings

The required input parameters could be hardcoded here but it is preferable to read them from environment vars due to:

  • Security (we will want to retrieve anything that could be sensitive from the repo Secrets)
  • Maintainability (by setting some parameters dynamically we can use the same code for multiple targets) 

Sign & Build Steps

The prepare_keychain lane will:

  • Create a temporary keychain
  • Import the Certificate and associated Private key from the local filesystem into the keychain

This lane is optional (we might not need it when running Fastlane on a machine where the right certificates are already installed)

The build_and_sign lane will:

  • Run cocoapods to install pod dependencies
  • Run xcodebuild against the desired scheme (passed as input param) to generate the .ipa file
  • Delete the temporary keychain (to avoid potential conflicts with future runs)

Publishing Steps

The publish_appstore lane will:

  • Generate a changelog from the git log
  • Authenticate to iTunes Connect and upload the .ipa file to TestFlight with associated metadata
  • Send a notification to the specified Slack channel informing that the build was successful and has been submitted (this is set to not fail the entire build if the webhook configuration is not valid)

Alternatively, we could have lanes for AdHoc distribution that send the .ipa elsewhere (such as S3).

Release Targets

The lanes we will invoke externally make use of the above lanes to build and release the specified target.

  • Before building, we run ensure_git_status_clean to make sure we are not including code that is not checked into the repo
  • The input parameters for the sign_and_build lane will be the scheme and desired export method (‘app-store or ‘ad-hoc’) which needs to match the Provisioning Profile we have selected for the target.
  • Before publishing to an App Store we can run additional steps such as tagging the release and committing the tag on the appropriate branch -see add_git_tag to adapt params as needed.
  • The input parameters for the publish_appstore lane will be the scheme -which corresponds to a registered app in the App Store.

The GitHub Actions Workflow

Now that we have our Fastlane configuration, we can validate it by running it locally. But we want to set this up so it runs automatically whenever we push to the right branches, and we do not want to tie up our development machine’s resources while this process runs.

This is where GitHub Actions comes in. The GitHub workflow file is checked into .github\workflows\dev_build.yml and performs the following steps:

  • Setup the required version of Node and install Node dependencies (for a React Native project)
  • Download the codesigning elements from S3 (certificate, private key, provisioning profile)
  • Generate the environment configuration file from values in Secrets
  • Call Fastlane to build and publish the app

Setting Up a Local Build Server

As mentioned before, the previous workflow could run on any GitHub macOS runner, but it would likely get stuck when attempting to log into TestFlight due to a 2FA token prompt.

The workaround we implemented is using any Mac we have physical access to as a self-hosted runner.

This not only spares us from having to generate session cookies but also allows us to use GitHub Actions without consuming the free minutes in our plan (MacOS runner minutes are expensive, counting as 10 Linux runner minutes each). For this we need to perform two simple steps:

  • Associate the device with the Apple ID used for submission, by logging into https://appleid.apple.com/ and entering the 2FA token from the device.
  • Setup the GH agent by following GitHub’s guide for self-hosted runners.
    • Organization owners can add self-hosted runners shared by multiple repos in an organization (keeping in mind job concurrency limits).
    • Otherwise, repo owners need to repeat the process of adding it individually for each repo (the same actual machine can still be reused for multiple projects).

Fortunately, there is no need to do any project-specific setup beyond this, as we can let GHA handle the build requirements (all official and third-party Actions are available to self-hosted runners).

We also do not need to give the machine a public IP address, as the agent installed during the setup will poll GH for kicking off the workflows and reporting back.

Upon setting up the runner, we can associate our workflows with it just by specifying its label in the on: section.

Some important configuration items:

Now, I am going to describe the approach we implemented for Android CI/CD, making use of Fastlane and a CI system (GitHub Actions). We used Amazon S3 to store signing artifacts, but any system where we can safely store encrypted files will work.

For this example, we’ll use an Android app developed with React Native, but the same approach works when using other languages supported by the Android SDK, such as Kotlin. The key assumption here is that we will use Gradle when building the APK.

Registering Apps

Within our Android project, we will define multiple build flavors, specified in our build.gradle file. For each of these, we need to register an application in the Google Play Console. After registering apps, we will need the following:

Both files should be placed in a secure location, with the credentials required to retrieve them stored in the repo Secrets.

Code Signing & API Keys

In order to distribute our app, our APK needs to be signed with a certificate generated by Google. Unlike iOS, Fastlane does not offer an equivalent to their match feature which can handle certificate creation and management end-to-end.

So, we need to generate it manually once from Android Studio, following the steps in their User Guide, and then store it somewhere our CICD can retrieve it.

For the latter, we will make use of AWS S3. This is a good option for us as we typically use AWS S3 in all our projects, and have to set AWS credentials in our working environment. One single bucket, encrypted with AWS KMS allows us to securely handle our Certificates, Keystores, and other sensitive files for all our projects.

In order to upload our APK via the Google Play Developer API, we also need an API JSON key file associated with a service account that will allow Fastlane to authenticate.

After creating one on the Google Play console, we can either store the entire JSON string as a Secret to retrieve as an environment variable, or do the same as with the Keystore, and place it on S3 for GitHub Actions to download and use during the build run (we will use the latter in this example).

Environment Variables

Our workflow should have the following sensitive keys defined as Secrets in the GitHub repo:

  • AWS keys (AWS_ACCESS_KEY_IDAWS_SECRET_ACCESS_KEY) associated with permissions to interact with the target bucket.
  • Keystore and Upload Key(Alias) name and passwords (ANDROID_RELEASE_STORE_PASSWORDANDROID_RELEASE_KEY_ALIASANDROID_RELEASE_KEY_PASSWORD)
  • Slack webhook URL and channel name (SLACK_URLSLACK_CHANNEL) for sending notifications upon build completion.

The Android Fastfile

Build Steps

This lane provides the generic steps to run the defined tasks for cleaning the build directory, installing Android dependencies, and building our APK for the desired flavor, using Gradlew:

Publish Steps

This lane retrieves the version and build number of our package and submits it to the Play Store, before finishing with a Slack notification that the release was successful:

Release Targets

After defining the generic steps for building and releasing, we can then reuse them for multiple flavors/targets by creating lanes for each:

Alternatively, we could define “debug only” lanes, which only run the build for local use without publishing, or store the APK on an alternate location (such as another S3 bucket).

The GitHub Actions Workflow

After we have a working Fastlane configuration, the next step is to tie it to a CI/CD system so the build runs automatically with every push to the right branches. This is how this looks for a React Native application using an Ubuntu runner in GitHub Actions:

In a nutshell, here is this workflow:

  • Checks out our code
  • Installs the required version of Node
  • Installs Node dependencies for the RN project
  • Downloads the Keystore and JSON API key file
  • Generates a .env file with all the environment variables Gradle will insert into the APK
  • Installs Fastlane and associated plugins (using Bundler)
  • Runs the corresponding Lane

Summary

In this piece, we looked at examples of how to automate mobile app deployments using Fastlane, a powerful free tool specifically designed for this.

We also showcased GitHub Actions as a good CI/CD system that can integrate with Fastlane to trigger our pipelines automatically and in a secure environment.

You can find complete Fastlane working examples in our Open Source boilerplate projects, Android Base and React Native Base.

All these cover just a couple of the many use cases you can apply these tools for – we highly recommend you to go through their extensive documentation sites.

Thanks for reading and stay tuned for more related content!

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DevOps Engineer at Rootstrap

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