Using dockerized container to build signed apk and a web to download the file

Building the image

The image at the docker hub, ichinosebinit/jenkins-flutter-android:latest has installed Android SDK, flutter and an image of an Android OS.

Steps

The jenkins image is pulled and flutter is installed.
The Flutter bin folder is setup in the path.
The default jdk is installed.
Android SDK is fetched and unzipped.
The contents of the Android SDK is managed, moved to a directory to be used by the Jenkins.
The licenses are accepted using the SDK manager.
The Android OS image is downloaded using the SDK manager.
The docker file is given here Docker File for Image creation.

Building the container to create and sign APKs

Pull the image from the dockerhub using,

docker pull ichinosebinit/jenkins-flutter-android:latest

Run the docker image using,

docker run -p 8070:8080 -v /D:/data:/var/jenkins_home ichinosebinit/jenkins-flutter-android:latest

Here, you can replace the port number i.e. 8070 to any one which is not allocated. But do not change the latter port number. The -v option refers to the mounted directory with the host and the container. Mount the preferred directory to the left side before ":" and leave the right mounted directories unchanged.

Run the docker container in the web browser

Open your web browser and open http://localhost:8070/ . Setup the Jenkins with admin password password given in log as initial password and install the necessary plugins.

Installing necessary plugins

Browse over to Manage Jenkins and go to Manage Plugins page. On the Available tab, search for GitLab plugin and Android Signing Plugin and install those plugins.

Adding Credentials

Go back to Manage Jenkins, head over to Manage Credentials under the Security section.
Under the Stores scoped to Jenkins section, click on Jenkins under the Store tab.
Select the Global credentials (unrestricted) and select Add Credentials in the left section of the page.

Adding GitLab Token

Select the GitLab API Token option under the Kind field.
Select the Global option under the Scope.
Paste the API Token from the GitLab of your account.
You can get your API Token from Gitlab Documentation
Give an unique ID for the Token.
Give a description for the Token.

Adding GitLab User ID

Select the Username with password option under the Kind field.
Select the Global option under the Scope.
Enter your Username of your GitLab account.
Enter your Password of your GitLab account.
Give an unique ID for the account.
Give a description for the account.

Note: The Id given here is used in the Jenkins pipeline script. So remember it or copy the ID for future use.

Adding a Android Signing Certificate

Select the Certificate option under the Kind field.
Select the Global option under the Scope.
Check the Upload PKCS#12 certificate radio button.
Select the file used for signing the APK.
Press the Change Password button.
Enter the password used while creating the certificate.
Give an unique ID for the account.
Give a description for the account.

Note: The Id given here is used in the Jenkins pipeline script. So remember it or copy the ID for future use.

Setting Environment Variables

Browse over to Manage Jenkins and go to Configure System page.
Head down and Check the Environment Variables checkbox under the heading Global Properties.
Click the Add button.
Add ANDROID_HOME as Name and /android-sdk as Value.
Click the Add button again.
Add HOME as Name and /root as Value.
Click the Apply button

Setting the GitLab Connection

Head down on the same page and under the heading Gitlab check the Enable authentication for '/project' end-point checkbox.
Enter the Connection Name.
Enter https://gitlab.com as Gitlab host URL.
Select the ID of the GitLab Connection using API Token previously saved in credentials.
Press the Test Connection button.
In case of Success, press the Save button. Else, check for permissions in your repository.

Changing the Jenkins file

Copy and paste the script from the Jenkinsfile in your editor.
In the stage git, change the branch name, credentialsId previously setup and url.
In the stage sign Android, change the keyStoreId previously setup in credentials.
Use the contents of the file in the next step.

Creating a new project

Select New Item and select Pipeline
Enter the name for your project. Avoid spaces if you can as it may lead to errors while mapping directories. The name for the project would be used later again.
Check the Discard old builds and enter 3 in Max # of builds to keep.
Under the GitLab Connection, select the Connection Name previously created.
Under the Build Triggers, select the Build when a change is pushed to GitLab. GitLab webhook checkbox.
Check the Poll SCM checkbox and enter * * * * * in the Schedule field.
Under the Pipeline section, copy and paste the jenkins script edited previously.
Press the Apply and Save button.

Building the APK

Browse the newly created job/item.
Click the Build Now option.
Wait for the Build to finish.

Building the container for web

Pull the image from the dockerhub using,

docker pull nginx:alpine

Run the docker image using,

The directory previously mounted needs to be given as the path.
Open the previously mounted directory path. Open workspace and then the project that was created.
Copy the path for the opened directory. e.g. /D:/data/workspace/easyshop/
Append the path build/app/outputs/flutter-apk with the previous path. e.g. /D:/data/workspace/easyshop/build/app/outputs/flutter-apk
Use the path in the left side of ":" in -v option.

Command for the nginx container

docker run -p 8060:80 -v "path":/usr/share/nginx/html nginx:alpine

Configuring the html file

Copy the web folder from the repository with index file, css and images directory.
Paste the contents of the web folder in the mounted directory in the host machine.
The path for the directory would be the path given while mounting.