Building and Deploying depending on front or backend changes in Gitlab - gitlab

Question

I'm starting to use gitlab CI/CD pipeline but have some doubts regarding the output of the building process if i was to have a project(Repo) and inside this project I have the front and backend separated by the project structure, ex:
CarProject
.gitlab-ci.yml
|__FrontEndCarProject
|__BackendCarProject
let's say that every time I change something in the frontend I would need to build it and deploy it to S3, but there is no need to build the backend (java application) and deploy it to elastic beanstalk (and vice versa for when i change the backend)..Is there a way to check where the changes have been made(FrontEndCarProject/BackendCarProject) using GitLab and redirect the .gitlab-ci.yml to a script file depending on if a have to deploy to S3 or elastic beanstalk?
Just trying
Note: another way is just to manually change the yml file depending on where i want to deploy..but is there a way to autodetect this and automated?
.gitlab-ci.yml
Just to get the idea, heres an example that would run in a linear way, but how can i conditionally build/deploy(depending on my front or backend)? should i keep them in different repos for simplicity? is it a good practice?
variables:
ARTIFACT_NAME: cars-api-v$CI_PIPELINE_IID.jar
APP_NAME: cars-api
stages:
- build
- deploy
# ONLY Build when front(FrontendCarProject) in changed
build_front:
stage: build
image: Node:latest
script:
- npm install
artifacts:
paths:
- ./dist
# ONLY build when backend(BackendCarProject) is changed
build_back:
stage: build
image: openjdk:12-alpine
script:
- ./gradlew build
artifacts:
paths:
- ./build/libs/
# ONLY deploy when front(FrontendCarProject) in changed
deploy_s3:
stage: deploy
image:
name: python:latest
script:
- aws configure set region us-east-1
- aws s3 cp ./build/libs/cars-api.jar s3://$S3_BUCKET/cars-api.jar
# ONLY deploy when backend(BackendCarProject) is changed
deploy_back_end:
stage: deploy
image:
name: banst/awscli
script:
- aws configure set region us-east-1
- aws s3 cp ./build/libs/$ARTIFACT_NAME s3://$S3_BUCKET/$ARTIFACT_NAME
- aws elasticbeanstalk create-application-version --application-name $APP_NAME --version-label $CI_PIPELINE_IID --source-bundle S3Bucket=$S3_BUCKET,S3Key=$ARTIFACT_NAME
- aws elasticbeanstalk update-environment --application-name $APP_NAME --environment-name "production" --version-label=$CI_PIPELINE_IID

Answer 1

If your frontend and backend can be built and deployed seperately, than you can use rules:changes to check if a change happened and need:optional to only deploy the respective built libraries.
variables:
ARTIFACT_NAME: cars-api-v$CI_PIPELINE_IID.jar
APP_NAME: cars-api
stages:
- build
- deploy
# ONLY Build when front(FrontendCarProject) in changed
build_front:
stage: build
image: Node:latest
script:
- npm install
rules:
- changes:
- FrontEndCarProject/*
artifacts:
paths:
- ./dist
# ONLY build when backend(BackendCarProject) is changed
build_back:
stage: build
image: openjdk:12-alpine
script:
- ./gradlew build
rules:
- changes:
- BackendEndCarProject/*
artifacts:
paths:
- ./build/libs/
# ONLY deploy when front(FrontendCarProject) in changed
deploy_s3:
stage: deploy
image:
name: python:latest
script:
- aws configure set region us-east-1
- aws s3 cp ./build/libs/cars-api.jar s3://$S3_BUCKET/cars-api.jar
needs:
- job: build_front
artifacts: true
optional: true
# ONLY deploy when backend(BackendCarProject) is changed
deploy_back_end:
stage: deploy
image:
name: banst/awscli
script:
- aws configure set region us-east-1
- aws s3 cp ./build/libs/$ARTIFACT_NAME s3://$S3_BUCKET/$ARTIFACT_NAME
- aws elasticbeanstalk create-application-version --application-name $APP_NAME --version-label $CI_PIPELINE_IID --source-bundle S3Bucket=$S3_BUCKET,S3Key=$ARTIFACT_NAME
- aws elasticbeanstalk update-environment --application-name $APP_NAME --environment-name "production" --version-label=$CI_PIPELINE_IID
needs:
- job: build_back
artifacts: true
optional: true