Measure process load with automatic handling of "Service Unavailable" plugin for Fastify.
It can check maxEventLoopDelay
, maxHeapUsedBytes
and maxRssBytes
values.
You can also specify custom health check, to verify the status of
external resources.
Fastify ^2.0.0. Please refer to this branch and related versions for Fastify ^1.1.0 compatibility.
npm i under-pressure --save
Require the plugin and register it into the Fastify instance.
const fastify = require('fastify')()
fastify.register(require('under-pressure'), {
maxEventLoopDelay: 1000,
maxHeapUsedBytes: 100000000,
maxRssBytes: 100000000
})
fastify.get('/', (req, reply) => {
reply.send({ hello: 'world'})
})
fastify.listen(3000, err => {
if (err) throw err
console.log(`server listening on ${fastify.server.address().port}`)
})
under-pressure
will automatically handle for you the Service Unavailable
error once one of the thresholds has been reached.
You can configure the error message and the Retry-After
header.
fastify.register(require('under-pressure'), {
maxEventLoopDelay: 1000,
message: 'Under pressure!',
retryAfter: 50
})
The default value for maxEventLoopDelay
, maxHeapUsedBytes
and maxRssBytes
is 0
.
If the value is 0
the check will not be performed.
Thanks to the encapsulation model of Fastify, you can selectively use this plugin in some subset of routes or even with different thresholds in different plugins.
This plugin also exposes a function that will tell you the current values of heapUsed
, rssBytes
and eventLoopDelay
.
console.log(fastify.memoryUsage())
If needed you can pass { exposeStatusRoute: true }
and under-pressure
will expose a /status
route for you that sends back a { status: 'ok' }
object. This can be useful if you need to attach the server to an ELB on AWS for example.
If you need the change the exposed route path, you can pass { exposeStatusRoute: '/alive' }
options.
If you need to pass options to the status route, such as logLevel or custom configuration you can pass an object,
fastify.register(require('under-pressure'), {
maxEventLoopDelay: 1000,
exposeStatusRoute: {
routeOpts: {
logLevel: 'debug',
config: {
someAttr: 'value'
}
},
url: '/alive' // If you also want to set a custom route path and pass options
}
})
The above example will set the logLevel
value for the /status
route be debug
.
If needed you can pass a custom healthCheck
property which is an async function and under-pressure
will allow you to check the status of other components of your service.
This function should return a promise which resolves to a boolean value. The healthCheck
function can be called either:
- every X milliseconds, the time can be
configured with the
healthCheckInterval
option. - every time the status route is called, if
exposeStatusRoute
is set totrue
.
By default when this function is supplied your service health is considered unhealthy, until it has started to return true.
const fastify = require('fastify')()
fastify.register(require('under-pressure'), {
healthCheck: async function () {
// do some magic to check if your db connection is healthy, etc...
return true
},
healthCheckInterval: 500
})
You can set a custom value for sampling the metrics returned by memoryUsage
using the sampleInterval
option, which accepts a number that represents the interval in milliseconds.
The default value is different depending on which Node version is used. On version 8 and 10 it is 5
, while on version 11.10.0 and up it is 1000
. This difference is due to the fact that from version 11.10.0 the event loop delay can be sampled with monitorEventLoopDelay
and this allows to increase the interval value.
const fastify = require('fastify')()
fastify.register(require('under-pressure'), {
sampleInterval: <your custom sample interval in ms>
})
This project is kindly sponsored by LetzDoIt.
Licensed under MIT.