MySQL adapters (@healthzkit/mysql)

The @healthzkit/mysql package provides HealthAdapter helpers for mysql (callback driver) and mysql2 (promise API). Successful checks run a lightweight SQL probe (default SELECT 1) and return ok with metadata.latencyMs plus any fields from an optional metadata hook; failures return fail with the caught error.

Install the adapter package and one database client:

pnpm add @healthzkit/mysql
# plus one of:
pnpm add mysql
pnpm add mysql2

mysql and mysql2 are optional peers-install the driver you use.

Package entrypoints

• @healthzkit/mysql - mysqlAdapter, mysql2Adapter, and their option types.
• @healthzkit/mysql/mysql - mysqlAdapter only.
• @healthzkit/mysql/mysql2 - mysql2Adapter only.

Use subpath imports when you want to avoid pulling both drivers into your bundle analysis path.

Shared options

Both factories share BaseMysqlOptions:

Option	Description
query	SQL string executed for the probe. Default SELECT 1.
metadata	Optional async (client) => Record<string, unknown> merged into check metadata with latencyMs.

Pass either connectionString or client (not both).

mysqlAdapter (mysql)

Peer: mysql >= 2.18.

Each check acquires a connection, runs connection.query(query), records round-trip latency, and **release()**s pooled connections in a finally block.

Connection string

Pass connectionString (and optional connectionOptions for extra pool settings). The adapter lazily imports mysql, parses a mysql:// or mysql2:// URL, and creates a shared internal Pool. Concurrent checks reuse that pool.

import { createHealthKit } from "healthzkit";
import { mysqlAdapter } from "@healthzkit/mysql";

const kit = createHealthKit({
  checks: [
    {
      name: "mysql",
      type: ["readiness"],
      adapter: mysqlAdapter({
        connectionString: process.env.DATABASE_URL!,
        connectionOptions: { connectTimeout: 2000 },
      }),
    },
  ],
});

Existing client or pool

Pass client as:

• A Pool: each check calls pool.getConnection(), runs the query, then releases the connection.
• A Connection: the query runs on that instance; release is a no-op when the connection has no release method.

import mysql from "mysql";
import { mysqlAdapter } from "@healthzkit/mysql/mysql";

const pool = mysql.createPool({
  host: "localhost",
  user: "app",
  database: "app",
});

const adapter = mysqlAdapter({
  client: pool,
  query: "SELECT VERSION()",
});

mysql2Adapter (mysql2)

Peer: mysql2 >= 3.

Uses the promise API from mysql2/promise. Each check acquires a connection, awaits connection.query(query), records latency, and releases pooled connections when applicable.

Connection string

Pass connectionString and connectionOptions (PoolOptions merged into the internal pool). The adapter lazily imports mysql2/promise, parses mysql:// or mysql2:// URLs, and reuses one internal pool across checks.

import { mysql2Adapter } from "@healthzkit/mysql/mysql2";

const adapter = mysql2Adapter({
  connectionString: process.env.DATABASE_URL!,
  connectionOptions: { connectionLimit: 2 },
});

Existing client or pool

Pass client as a Pool or Connection from your app.

import mysql from "mysql2/promise";
import { mysql2Adapter } from "@healthzkit/mysql";

const pool = mysql.createPool(process.env.DATABASE_URL!);

const adapter = mysql2Adapter({
  client: pool,
  metadata: async () => ({ driver: "mysql2" }),
});

Connection strings

Both adapters accept URLs with the mysql:// or mysql2:// scheme (default port 3306). Userinfo and database name come from the URL; additional pool settings go in connectionOptions.

mysql://user:pass@db.example:3306/myapp
mysql2://localhost:3307/myapp

Scheduling

For busy databases, pair these adapters with a schedule on the check so readiness reads cached results (see Scheduling).