Maven & GitLab CI setup to deploy to a Nexus server

.gitlab-ci.yml

variables:
  NEXUS_URL: XXX
  NEXUS_USER: XXX
  NEXUS_PWD: XXX
  SNAPSHOT_DEPLOYMENT_REPOSITORY: ${NEXUS_URL}/repository/maven-snapshots/
  RELEASE_DEPLOYMENT_REPOSITORY: ${NEXUS_URL}/repository/maven-releases/
  MAVEN_CLI_OPTS: "-s .m2/settings.xml --batch-mode --errors --fail-at-end --show-version"
  MAVEN_CLI_POST_OPTS: "-Dnexus.url=${NEXUS_URL} -Dmaven.repo.local=.m2"

deploy:
  stage: deploy
  image: maven:3.5.3-alpine
  script:
    # source:jar attach source and javadoc artifacts
    - mvn $MAVEN_CLI_OPTS source:jar deploy -Dnexus_user=${NEXUS_USER} -Dnexus_pwd=${NEXUS_PWD} -DsnapshotDeploymentRepository=$SNAPSHOT_DEPLOYMENT_REPOSITORY -DreleaseDeploymentRepository=$RELEASE_DEPLOYMENT_REPOSITORY -DskipTests ${MAVEN_CLI_POST_OPTS}
  only:
    - master

.m2_settings.xml

<?xml version="1.0" encoding="UTF-8"?>
<settings xmlns="http://maven.apache.org/SETTINGS/1.0.0"
          xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
          xsi:schemaLocation="http://maven.apache.org/SETTINGS/1.0.0 http://maven.apache.org/xsd/settings-1.0.0.xsd">
    <servers>
        <server>
            <id>nexus-snapshots</id>
            <username>${nexus_user}</username>
            <password>${nexus_pwd}</password>
        </server>
        <server>
            <id>nexus-releases</id>
            <username>${nexus_user}</username>
            <password>${nexus_pwd}</password>
        </server>
    </servers>
</settings>

pom.xml

<project>
    <distributionManagement>
        <snapshotRepository>
            <id>nexus-snapshots</id>
            <url>${nexus.url}/repository/maven-snapshots/</url>
        </snapshotRepository>
        <repository>
            <id>nexus-releases</id>
            <url>${nexus.url}/repository/maven-releases/</url>
        </repository>
    </distributionManagement>
</project>