Add MySQL example.

.github/workflows/mysql-service.yml

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+name: MySQL Service Example
+
+on:
+  push:
+    branches:
+    - main
+  pull_request:
+    branches:
+    - main
+
+defaults:
+  run:
+    working-directory: ./mysql
+
+jobs:
+  container-job:
+    runs-on: ubuntu-latest
+
+    # runs all of the steps inside the specified container rather than on the VM host.
+    # Because of this the network configuration changes from host based network to a container network.
+    container:
+      image:  node:10.16-jessie
+
+    services:
+      mysql:
+        image: mysql:5.7
+        env:
+          MYSQL_ALLOW_EMPTY_PASSWORD: yes
+        ports:
+        - 3306:3306
+        # needed because the mysql container does not provide a healthcheck
+        options: --health-cmd="mysqladmin ping" --health-interval=10s --health-timeout=10s --health-retries=10
+
+    steps:
+    - uses: actions/checkout@v2
+    - run: npm ci
+    - run: node client.js
+      env:
+        # use mysql for the host here because we have specified a container for the job.
+        # If we were running the job on the VM this would be localhost
+        MYSQL_HOST: mysql
+        MYSQL_PORT: ${{ job.services.mysql.ports[3306] }}
+
+  # Runs all steps on the VM
+  # The service containers will use host port binding instead of container networking so you access them via localhost rather than the service name
+  vm-job:
+    runs-on: ubuntu-latest
+
+    services:
+      mysql:
+        image: mysql:5.7
+        env:
+          MYSQL_ALLOW_EMPTY_PASSWORD: yes
+        ports:
+        # will assign a random free host port
+        - 3306/tcp
+        # needed because the mysql container does not provide a healthcheck
+        options: --health-cmd="mysqladmin ping" --health-interval=10s --health-timeout=10s --health-retries=10
+
+    steps:
+    - uses: actions/checkout@v2
+    - run: npm ci
+    - run: node client.js
+      env:
+        # use localhost for the host here because we are running the job on the VM.
+        # If we were running the job on in a container this would be mysql
+        MYSQL_HOST: localhost
+        MYSQL_PORT: ${{ job.services.mysql.ports[3306] }} # get randomly assigned published port

mysql/client.js

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+const mysql = require('mysql');
+
+const mysqlConnection = mysql.createConnection({
+  host: process.env.MYSQL_HOST,
+  port: process.env.MYSQL_PORT,
+  user: 'root',
+  password: '',
+  database: 'mysql'
+});
+
+mysqlConnection.connect();
+
+mysqlConnection.query('SELECT NOW()', (err, res) => {
+  if (err) throw err
+  console.log(res)
+  mysqlConnection.end()
+});

mysql/package.json

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+{
+  "dependencies": {
+    "mysql": "^2.18.1"
+  }
+}