AWS CodeBuild

Core concept: CodeBuild is a fully managed continuous integration service — no Jenkins servers to maintain.

buildspec.yml Reference

version: 0.2

run-as: root

env:
  variables:           # Plaintext env vars (visible in console)
    JAVA_HOME: "/usr/lib/jvm/java-17"
    
  parameter-store:     # Fetched from SSM at build start
    DB_URL: "/prod/myapp/db-url"
    
  secrets-manager:     # Fetched from Secrets Manager at build start
    DB_PASSWORD: "prod/myapp/db:password"
    API_KEY: "prod/myapp/api-key:key"

  exported-variables:  # Available to downstream CodePipeline stages
    - IMAGE_TAG

phases:
  install:
    runtime-versions:
      java: corretto17
    commands:
      - echo "Installing tools..."
      
  pre_build:
    commands:
      - echo "Logging in to ECR..."
      - aws ecr get-login-password --region $AWS_DEFAULT_REGION | docker login ...
      - export IMAGE_TAG=$(echo $CODEBUILD_RESOLVED_SOURCE_VERSION | cut -c 1-7)

  build:
    commands:
      - echo "Build started on `date`"
      - mvn clean verify    # Compile + test + package
      - docker build -t my-app:$IMAGE_TAG .

  post_build:
    on-failure: ABORT    # ABORT or CONTINUE
    commands:
      - echo "Pushing image..."
      - docker push $ECR_REPO:$IMAGE_TAG
      - printf '[{"name":"app","imageUri":"%s"}]' $ECR_REPO:$IMAGE_TAG > imagedefinitions.json

artifacts:
  files:
    - imagedefinitions.json
    - appspec.yaml
    - taskdef.json
  name: BuildOutput

secondary-artifacts:
  TestReports:
    files:
      - target/surefire-reports/**/*.xml
    discard-paths: no

reports:
  SurefireReports:
    files:
      - "target/surefire-reports/**/*.xml"
    file-format: JUNITXML
    discard-paths: no

cache:
  paths:
    - '/root/.m2/**/*'        # Maven local repo
    - '/root/.gradle/**/*'    # Gradle cache

Built-in Environment Variables

Variable	Value
`AWS_DEFAULT_REGION`	Region of the build
`AWS_ACCOUNT_ID`	Account ID
`CODEBUILD_BUILD_ID`	Unique build ID
`CODEBUILD_RESOLVED_SOURCE_VERSION`	Git commit SHA
`CODEBUILD_SOURCE_REPO_URL`	Source repository URL

Caching

Cache Type	Location	Best For
Local	Build host (cleared between hosts)	Fast single-host builds
S3	Persisted across builds	Maven/Gradle dependencies

cache:
  type: S3
  location: my-bucket/codebuild-cache
  paths:
    - '/root/.m2/**/*'

VPC Support

For builds that need to access private resources (RDS, ElastiCache, internal APIs):

# CloudFormation
CodeBuildProject:
  Type: AWS::CodeBuild::Project
  Properties:
    VpcConfig:
      VpcId: !Ref VPC
      Subnets: [!Ref PrivateSubnet1, !Ref PrivateSubnet2]
      SecurityGroupIds: [!Ref BuildSecurityGroup]

NAT Gateway required

Builds in a VPC cannot reach the internet (for pulling Docker images, downloading Maven artifacts) unless a NAT Gateway is configured in the VPC.

Test Reports

reports:
  MyTestReports:
    files:
      - "**/*.xml"
    base-directory: target/surefire-reports
    file-format: JUNITXML  # Or CUCUMBERJSON, TESTNGXML, VISUALSTUDIOTRX

Reports appear in the CodeBuild console with pass/fail trends.

DVA-C02 Exam Tips

Quick Exam Rules

VPC and Internet Access: If a CodeBuild project is connected to a VPC (to access private DBs), it loses internet access by default. You MUST add a NAT Gateway to the VPC for it to reach external APIs or pull public docker images.
buildspec.yml location: By default, it must be in the root of the source directory, but you can override the filename and path in the project configuration.
Caching: Always cache Maven (/root/.m2/**/*) or Docker layers to S3 to reduce build times.
Artifacts: CodeBuild can upload artifacts to S3 or CodePipeline. Use imagedefinitions.json for ECS deployments.
Environment Variables: Use parameter-store or secrets-manager for sensitive values instead of plaintext variables.

Practice Questions

Q1. A CodeBuild project needs to access a private RDS instance during integration tests. What configuration is required?

A) Use RDS public endpoint
B) Configure VPC settings (VPC, Subnets, Security Groups) on the CodeBuild project
C) Allow 0.0.0.0/0 in the RDS security group
D) Use RDS IAM Authentication

✅ Answer & Explanation

B — Configure VPC, subnets, and security groups on the CodeBuild project. The build environment runs inside your VPC and can access private resources. Add a NAT Gateway if the build also needs internet access.

Q2. A developer wants to speed up Maven builds by reusing downloaded dependencies between builds. What should they configure?

A) Increase CodeBuild compute size
B) Use a custom Docker image with pre-installed dependencies
C) Configure S3 cache for /root/.m2/**/*
D) Use buildspec install phase to pre-download

✅ Answer & Explanation

C — S3 caching persists the Maven local repository between builds. CodeBuild uploads the cache to S3 after each build and downloads it at the start, dramatically reducing dependency download time.

Resources

Interview Questions

How do you optimize CodeBuild cost and throughput for large monorepos with mixed Java and container builds?
When a build runs in private subnets, what networking design avoids flaky internet dependency failures?
Which secrets strategy do you use in buildspec to balance security, auditability, and developer velocity?
How would you harden build reproducibility so two builds from the same commit produce equivalent artifacts?

Short answer guide:

Use targeted build matrices, caching, and right-sized compute classes.
Provide NAT or VPC endpoints for required services and deterministic dependency mirrors.
Prefer SSM/Secrets Manager references, avoid plaintext env variables.
Pin toolchain versions and isolate mutable external inputs.