A module for managing MySQL connections at serverless scale.
npm install serverless-mysql
Serverless MySQL is a wrapper for Doug Wilson's amazing mysql2 Node.js module. Normally, using the mysql2 module with Node apps would be just fine. However, serverless functions (like AWS Lambda, Google Cloud Functions, and Azure Functions) scale almost infinitely by creating separate instances for each concurrent user. This is a MAJOR PROBLEM for RDBS solutions like MySQL, because available connections can be quickly maxed out by competing functions. Not anymore. 😀
Serverless MySQL adds a connection management component to the mysql2 module that is designed specifically for use with serverless applications. This module constantly monitors the number of connections being utilized, and then based on your settings, manages those connections to allow thousands of concurrent executions to share them. It will clean up zombies, enforce connection limits per user, and retry connections using trusted backoff algorithms.
In addition, Serverless MySQL also adds modern async/await support to the mysql2 module, eliminating callback hell or the need to wrap calls in promises. It also dramatically simplifies transactions, giving you a simple and consistent pattern to handle common workflows.
NOTE: This module should work with any standards-based MySQL server. It has been tested with AWS's RDS MySQL, Aurora MySQL, and Aurora Serverless.
``javascript
// Require and initialize outside of your main handler
const mysql = require('serverless-mysql')({
config: {
host : process.env.ENDPOINT,
database : process.env.DATABASE,
user : process.env.USERNAME,
password : process.env.PASSWORD
}
})
// Main handler function
exports.handler = async (event, context) => {
// Run your query
let results = await mysql.query('SELECT * FROM table')
// Run clean up function
await mysql.end()
// Return the results
return results
}
`
You can enable logging of the final SQL query (with all parameter values substituted) by setting the returnFinalSqlQuery option to true:
`javascript
// Require and initialize outside of your main handler
const mysql = require('serverless-mysql')({
config: {
host : process.env.ENDPOINT,
database : process.env.DATABASE,
user : process.env.USERNAME,
password : process.env.PASSWORD
},
returnFinalSqlQuery: true // Enable SQL query logging
})
// Main handler function
exports.handler = async (event, context) => {
// Run your query with parameters
const results = await mysql.query('SELECT * FROM users WHERE id = ?', [userId])
// Access the SQL query with substituted values
console.log('Executed query:', results.sql)
// Run clean up function
await mysql.end()
// Return the results
return results
}
`
When returnFinalSqlQuery is enabled, the SQL query with substituted values is also attached to error objects when a query fails, making it easier to debug:
`javascript`
try {
const results = await mysql.query('SELECT * FROM nonexistent_table')
} catch (error) {
// The error object will have the SQL property
console.error('Failed query:', error.sql)
console.error('Error message:', error.message)
}
npm i serverless-mysql
Requirements
- Node 8.10+
- MySQL server/clusterConsiderations for this module
- Return promises for easy async request handling
- Exponential backoff (using Jitter) to handle failed connections
- Monitor active connections and disconnect if more than X% of connections are being used
- Support transactions
- Support JIT connections
- Assume AWS endorsed best practices from hereHow to use this module
Serverless MySQL wraps the mysql module, so this module supports pretty much everything that the module does. It uses all the same connection options, provides a query() method that accepts the same arguments when performing queries (except the callback), and passes back the query results exactly as the mysql2 module returns them. There are a few things that don't make sense in serverless environments, like streaming rows, so there is no support for that yet.To use Serverless MySQL, require it OUTSIDE your main function handler. This will allow for connection reuse between executions. The module must be initialized before its methods are available. Configuration options must be passed in during initialization.
`javascript
// Require and initialize with default options
const mysql = require('serverless-mysql')() // <-- initialize with function call// OR include configuration options
const mysql = require('serverless-mysql')({
backoff: 'decorrelated',
base: 5,
cap: 200
})
`MySQL connection options can be passed in at initialization or later using the
method.`javascript
mysql.config({
host : process.env.ENDPOINT,
database : process.env.DATABASE,
user : process.env.USERNAME,
password : process.env.PASSWORD
})
`You can explicitly establish a connection using the
method if you want to, though it isn't necessary. This method returns a promise, so you'll need to await the response or wrap it in a promise chain.`javascript
await mysql.connect()
`Running queries is super simple using the
method. It supports all query options supported by the mysql2 module, but returns a promise instead of using the standard callbacks. You either need to await them or wrap them in a promise chain.`javascript
// Simple query
let results = await query('SELECT * FROM table')// Query with placeholder values
let results = await query('SELECT * FROM table WHERE name = ?', ['serverless'])
// Query with advanced options
let results = await query({
sql: 'SELECT * FROM table WHERE name = ?',
timeout: 10000,
values: ['serverless']
})
`Once you've run all your queries and your serverless function is ready to return data, call the
method to perform connection management. This will do things like check the current number of connections, clean up zombies, or even disconnect if there are too many connections being used. Be sure to await its results before continuing.`javascript
// Perform connection management tasks
await mysql.end()
`Note that
will NOT necessarily terminate the connection. Only if it has to to manage the connections. If you'd like to explicitly terminate connections, use the quit() method.`javascript
// Gracefully terminate the connection
mysql.quit()
`If you need access to the
object, you can use the getClient() method. This will allow you to use any supported feature of the mysql2 module directly.`javascript
// Connect to your MySQL instance first
await mysql.connect()
// Get the connection object
let connection = mysql.getClient()// Use it to escape a value
let value = connection.escape('Some value to be escaped')
`You can change the user of an existing connection using the
method. This is useful when you need to switch to a different MySQL user with different permissions.`javascript
// Change to a different user
await mysql.changeUser({
user: 'newuser',
password: 'newpassword'
})// Now queries will be executed as the new user
let results = await mysql.query('SELECT * FROM restricted_table')
`You can also use the
method to change the current database, which is equivalent to the USE DATABASE SQL statement:`javascript
// Change to a different database
await mysql.changeUser({
database: 'new_database' // Change the database only
})// Now queries will be executed against the new database
let results = await mysql.query('SELECT * FROM new_database_table')
`Alternatively, you can use the standard SQL
statement with the query() method:`javascript
// Change to a different database using SQL
await mysql.query('USE new_database')// Now queries will be executed against the new database
let results = await mysql.query('SELECT * FROM new_database_table')
`Configuration Options
There are two ways to provide a configuration.
The one way is using a connection string at initialization time.
javascript
const mysql = require('serverless-mysql')(mysql://${process.env.USERNAME}:${process.env.PASSWORD}@${process.env.ENDPOINT}:${process.env.PORT}/${process.env.DATABASE})
`The other way is to pass in the options defined in the below table.
Below is a table containing all of the possible configuration options for
. Additional details are provided throughout the documentation.| Property | Type | Description | Default |
| -------- | ---- | ----------- | ------- |
| library |
Function | Custom mysql library | require('mysql2') |
| promise | Function | Custom promise library | Promise |
| backoff | String or Function | Backoff algorithm to be used when retrying connections. Possible values are full and decorrelated, or you can also specify your own algorithm. See Connection Backoff for more information. | full |
| base | Integer | Number of milliseconds added to random backoff values. | 2 |
| cap | Integer | Maximum number of milliseconds between connection retries. | 100 |
| config | Object | A mysql2 configuration object as defined here | {} |
| connUtilization | Number | The percentage of total connections to use when connecting to your MySQL server. A value of 0.75 would use 75% of your total available connections. | 0.8 |
| manageConns | Boolean | Flag indicating whether or not you want serverless-mysql to manage MySQL connections for you. | true |
| maxConnsFreq | Integer | The number of milliseconds to cache lookups of @@max_connections. | 15000 |
| maxRetries | Integer | Maximum number of times to retry a connection before throwing an error. | 50 |
| onError | function | Event callback when the MySQL connection fires an error. | |
| onClose | function | Event callback when MySQL connections are explicitly closed. | |
| onConnect | function | Event callback when connections are succesfully established. | |
| onConnectError | function | Event callback when connection fails. | |
| onKill | function | Event callback when connections are explicitly killed. | |
| onKillError | function | Event callback when a connection cannot be killed. | |
| onRetry | function | Event callback when connections are retried. | |
| usedConnsFreq | Integer | The number of milliseconds to cache lookups of current connection usage. | 0 |
| zombieMaxTimeout | Integer | The maximum number of seconds that a connection can stay idle before being recycled. | 900 |
| zombieMinTimeout | Integer | The minimum number of seconds that a connection must be idle before the module will recycle it. | 3 |
| returnFinalSqlQuery | Boolean | Flag indicating whether to attach the final SQL query (with substituted values) to the results. When enabled, the SQL query will be available as a non-enumerable sql property on array results or as a regular property on object results. | false |
| maxQueryRetries | Integer | Maximum number of times to retry a query before giving up. | 0 |
| queryRetryBackoff | String or Function | Backoff algorithm to be used when retrying queries. Possible values are full and decorrelated, or you can also specify your own algorithm. See Connection Backoff for more information. | full |
| onQueryRetry | function | Event callback when queries are retried. | |$3
If manageConns is not set to false, then this module will automatically kill idle connections or disconnect the current connection if the connUtilization limit is reached. Even with this aggressive strategy, it is possible that multiple functions will be competing for available connections. The backoff setting uses the strategy outlined here to use Jitter instead of Exponential Backoff when attempting connection retries.The two supported methods are
full and decorrelated Jitter. Both are effective in reducing server strain and minimize retries. The module defaults to full.Full Jitter: LESS work, MORE time
`javascript
sleep = random_between(0, min(cap, base 2 * attempts))
`Decorrelated Jitter: MORE work, LESS time
javascript
sleep = min(cap, random_between(base, sleep * 3))
`In addition to the two built-in algorithms, you can also provide your own by setting the value of
to an anonymous function. The function will receive the last wait value (how long the previous connection delay was) and retries (the number of retries attempted). Your function must return an Integer that represents the number of milliseconds to delay the next retry.`javascript
backoff: (wait,retries) => {
console.log('CUSTOM BACKOFF',wait,retries)
return 20 // return integer
}
`Custom libraries
Set your own promise library
javascript
promise: require('bluebird')
`Set your own mysql library, wrapped with AWS x-ray for instance
javascript
library: require('aws-sdk-xray-node')(require('mysql2'));
`$3
Currently, our type definitions rely on the module.
In order to use a custom library, you will need to do something along the following snippet:`typescript
import * as serverlessMysql from 'serverless-mysql';
import * as mysql2 from 'mysql2';const slsMysql = serverlessMysql({
library: mysql2 as any
})
// OR
const slsMysql = serverlessMysql({
// @ts-ignore
library: mysql2
})
`Events
The module fires seven different types of events: , onConnectError, onRetry, onClose, onError, onKill, and onKillError. These are reporting events that allow you to add logging or perform additional actions. You could use these events to short-circuit your handler execution, but using catch blocks is preferred. For example, onError and onKillError are not fatal and will be handled by serverless-mysql. Therefore, they will NOT throw an error and trigger a catch block.Error events (
onConnectError, onError and onKillError) all receive one argument containing the mysql2 module error object.`javascript
onConnectError: (e) => { console.log('Connect Error: ' + e.code) }
`The
event recieves the MySQL connection object, onKill receives the threadId of the connection killed, and onClose doesn't receive any arguments.onRetry receives four arguments. The error object, the number of retries, the delay until the next retry, and the backoff algorithm used (full, decorrelated or custom).`javascript
onRetry: (err,retries,delay,type) => { console.log('RETRY') }
` also receives four arguments. The error object, the number of retries, the delay until the next retry, and the backoff algorithm used (full, decorrelated or custom).`javascript
onQueryRetry: (err,retries,delay,type) => { console.log('QUERY RETRY') }
`MySQL Server Configuration
There really isn't anything special that needs to be done in order for your MySQL server (including RDS, Aurora, and Aurora Serverless) to use . You should just be aware of the following two scenarios.If you set max
user_connections, the module will only manage connections for that user. This is useful if you have multiple clients connecting to the same MySQL server (or cluster) and you want to make sure your serverless app doesn't use all of the available connections.If you're not setting max
user_connections, the user MUST BE granted the PROCESS privilege in order to count other connections. Otherwise it will assume that its connections are the only ones being used. Granting PROCESS is fairly safe as it is a read only permission and doesn't expose any sensitive data.Query Timeouts
The mysql2 module allows you to specify a "timeout" with each query. Typically this will disconnect the connection and prevent you from running additional queries. serverless-mysql handles timeouts a bit more elegantly by throwing an error and destroy()ing the connection. This will reset the connection completely, allowing you to run additional queries AFTER you catch the error.Transaction Support
Transaction support in serverless-mysql has been dramatically simplified. Start a new transaction using the transaction() method, and then chain queries using the query() method. The query() method supports all standard query options. Alternatively, you can specify a function as the only argument in a query() method call and return the arguments as an array of values. The function receives two arguments, the result of the last query executed and an array containing all the previous query results. This is useful if you need values from a previous query as part of your transaction.You can specify an optional
rollback() method in the chain. This will receive the error object, allowing you to add additional logging or perform some other action. Call the commit() method when you are ready to execute the queries.`javascript
let results = await mysql.transaction()
.query('INSERT INTO table (x) VALUES(?)', [1])
.query('UPDATE table SET x = 1')
.rollback(e => { / do something with the error / }) // optional
.commit() // execute the queries
`With a function to get the
from the previous query:`javascript
let results = await mysql.transaction()
.query('INSERT INTO table (x) VALUES(?)', [1])
.query((r) => ['UPDATE table SET x = 1 WHERE id = ?', r.insertId])
.rollback(e => { / do something with the error / }) // optional
.commit() // execute the queries
`You can also return a
or empty response from .query() calls within a transaction. This lets you perform conditional transactions like this:`javascript
let results = await mysql.transaction()
.query('DELETE FROM table WHERE id = ?', [someVar])
.query((r) => {
if (r.affectedRows > 0) {
return ['UPDATE anotherTable SET x = 1 WHERE id = ?', [someVar]]
} else {
return null
}
})
.rollback(e => { / do something with the error / }) // optional
.commit() // execute the queries
`If the record to
doesn't exist, the UPDATE will not be performed. If the UPDATE fails, the DELETE will be rolled back.NOTE: Transaction support is designed for InnoDB tables (default). Other table types may not behave as expected.
Reusing Persistent Connections
If you're using AWS Lambda with callbacks, be sure to set context.callbackWaitsForEmptyEventLoop = false; in your main handler. This will allow the freezing of connections and will prevent Lambda from hanging on open connections. See here for more information. If you are using async functions, this is no longer necessary.Tests
I've run a lot of tests using a number of different configurations. Ramp ups appear to work best, but once there are several warm containers, the response times are much better. Below is an example test I ran using AWS Lambda and Aurora Serverless. Aurora Serverless was configured with 2 ACUs (and it didn't autoscale), so there were only 90 connections available to the MySQL cluster. The Lambda function was configured with 1,024 MB of memory. This test simulated 500 users per second for one minute. Each user ran a sample query retrieving a few rows from a table.From the graph below you can see that the average response time was 41 ms (min 20 ms, max 3743 ms) with ZERO errors.
!Serverless MySQL test - 500 connections per second w/ 90 connections available
Other tests that use larger configurations were extremely successful too, but I'd appreciate other independent tests to verify my assumptions.
Contributions
Contributions, ideas and bug reports are welcome and greatly appreciated. Please add issues for suggestions and bug reports or create a pull request.Query Retries
The module supports automatic retries for transient query errors. When a query fails with a retryable error (such as deadlocks, timeouts, or connection issues), the module will automatically retry the query using the configured backoff strategy.By default, query retries are disabled (maxQueryRetries = 0) for backward compatibility with previous versions. To enable this feature, set
maxQueryRetries to a value greater than 0.You can configure the maximum number of retries with the
maxQueryRetries option (default: 0) and the backoff strategy with the queryRetryBackoff option (default: 'full'). The module will use the same backoff algorithms as for connection retries.`javascript
const mysql = require('serverless-mysql')({
config: {
host: process.env.ENDPOINT,
database: process.env.DATABASE,
user: process.env.USERNAME,
password: process.env.PASSWORD
},
maxQueryRetries: 5, // Enable query retries with 5 maximum attempts
queryRetryBackoff: 'decorrelated',
onQueryRetry: (err, retries, delay, type) => {
console.log(Retrying query after error: ${err.code}, attempt: ${retries}, delay: ${delay}ms)
}
})
``