@bufferapp/ekg
v0.1.2
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Health and liveness checks
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EKG
EKG is a library for implementing Kubernetes liveness and readiness probe handlers in a sidecar or in your application.
NOTE: This project was heavily influenced from Heptio Healthcheck. However EKG takes it a step further by providing a configurable sidecar. This means that for the most common healthcheck scenarios you don't need to instrument you application with code -- you can write the healthcheck configurations in YAML.
Quickstart - Kubernetes
The fastest way to get up an running with EKG is to add a it as a sidecar in the Kubernetes deployment file.
apiVersion: extensions/v1beta1
kind: Deployment
metadata:
name: my-application
spec:
replicas: 1
template:
metadata:
labels:
app: my-application
spec:
containers:
- name: my-application
image: my-org/my-application
ports:
- containerPort: 3000
# add the sidecar
- name: healthcheck
image: bufferapp/ekg:0.1.1
env:
- name: EKG_CONFIG
value: >
{
"port": 8086,
"livenessChecks": [
{
"name": "httpget-check-service",
"type": "httpGetCheck",
"url": "http://localhost:3000"
}
],
"readinessChecks": [
{
"name": "dns-check-upstream",
"type": "dnsResolveCheck",
"host": "upstream.example.com"
},
{
"name": "mongodb-check-buffer",
"type": "mongoDBCheck",
"host": "mongo",
"port": 27017
}
]
}
# define a liveness probe that checks every 5 seconds, starting after 5 seconds
livenessProbe:
httpGet:
path: /live
port: 8086
initialDelaySeconds: 5
periodSeconds: 5
# define a readiness probe that checks every 5 seconds
readinessProbe:
httpGet:
path: /ready
port: 8086
periodSeconds: 5
Sidecar Config API
EKG sidecar is passed it's configuration as JSON through the EKG_CONFIG environment variable. It has the following configuration options:
{
"port": 8086,
"livenessChecks": [
{
"name": "httpget-check-service",
"type": "httpGetCheck",
"url": "http://localhost:3000",
"timeout": 5000
},
{
"name": "dns-check-upstream",
"type": "dnsResolveCheck",
"host": "upstream.example.com",
"timeout": 5000
},
{
"name": "tcp-check-buffer",
"type": "tcpDialCheck",
"host": "buffer.com",
"port": 80,
"timeout": 5000
},
{
"name": "mongodb-check-buffer",
"type": "mongoDBCheck",
"host": "mongo",
"port": 27017,
"timeout": 5000
}
],
"readinessChecks": [
{
"name": "httpget-check-service",
"type": "httpGetCheck",
"url": "http://localhost:3000",
"timeout": 5000
},
{
"name": "dns-check-upstream",
"type": "dnsResolveCheck",
"host": "upstream.example.com",
"timeout": 5000
},
{
"name": "tcp-check-buffer",
"type": "tcpDialCheck",
"host": "buffer.com",
"port": 80,
"timeout": 5000
},
{
"name": "mongodb-check-buffer",
"type": "mongoDBCheck",
"host": "mongo",
"port": 27017,
"timeout": 5000
}
]
}
port
An integer specifying the port to serve the liveness and readiness probes.
livenessChecks
A list of checks to perform when the /live
endpoint is requested.
readinessChecks
A list of checks to perform when the /ready
endpoint is requested.
There are several types of checks that can be configured:
Check Types
There are several different types of checks that can be configured. Each check is performed serially and in order. Both livenessChecks and readinessChecks can handle all configurable checks:
httpGetCheck
perform an HTTP get request against a url
{
"name": "httpget-check-service", //
"type": "httpGetCheck",
"url": "http://localhost:3000",
"timeout": 5000
}
dnsResolveCheck
Do a DNS lookup on a host
{
"name": "dns-check-upstream",
"type": "dnsResolveCheck",
"host": "upstream.example.com",
"timeout": 5000
}
tcpDialCheck
Attempt to establish a TCP socket connection
{
"name": "tcp-check-buffer",
"type": "tcpDialCheck",
"host": "buffer.com",
"port": 80,
"timeout": 5000
}
mongoDBCheck
Ping a mongodb database
{
"name": "mongodb-check-buffer",
"type": "mongoDBCheck",
"host": "mongo",
"port": 27017,
"timeout": 5000
}
Secrets
You might want configure a healthcheck on a public repository with a URL that could be considered sensitive. EKG can plug environment variables into the EKG_CONFIG environment for this type of information:
apiVersion: extensions/v1beta1
kind: Deployment
metadata:
name: my-application
spec:
replicas: 1
template:
metadata:
labels:
app: my-application
spec:
containers:
- name: my-application
image: my-org/my-application
ports:
- containerPort: 3000
# add the sidecar
- name: healthcheck
image: bufferapp/ekg:0.1.1
env:
# my super secret MongoDB host
- name: MONGO_HOST
valueFrom:
secretKeyRef:
key: mongo-host
name: my-application-secrets
# my super secret MongoDB port
- name: MONGO_PORT
valueFrom:
secretKeyRef:
key: mongo-port
name: my-application-secrets
- name: EKG_CONFIG
value: >
{
"port": 8086,
"livenessChecks": [
{
"name": "httpget-check-service",
"type": "httpGetCheck",
"url": "http://localhost:3000"
}
],
"readinessChecks": [
{
"name": "dns-check-upstream",
"type": "dnsResolveCheck",
"host": "upstream.example.com"
},
{
"name": "mongodb-check-buffer",
"type": "mongoDBCheck",
# Plug in mongo secrets
"host": "${MONGO_HOST}",
"port": ${MONGO_PORT}
}
]
}
# define a liveness probe that checks every 5 seconds, starting after 5 seconds
livenessProbe:
httpGet:
path: /live
port: 8086
initialDelaySeconds: 5
periodSeconds: 5
# define a readiness probe that checks every 5 seconds
readinessProbe:
httpGet:
path: /ready
port: 8086
periodSeconds: 5
Quickstart - Manual
If you don't want to use a sidecar or have some custom liveness checks you'd like to perform, this is the better option. The easiest way to get going is to add some checks and listen on a port the main application is not using.
EKG is an NPM package for Node applications. Add it as a dependency to your package.json:
npm i -S @bufferapp/ekg
Instrument EKG into your app.
const micro = require('micro')
const EKG = require('@bufferapp/ekg')
const mainServer = micro(() => 'OK')
mainServer.listen(3000, () => console.log('main - listening on port 3000'))
const ekg = new EKG()
// Liveness
ekg.addLivenessCheck({
name: 'passing-live-check',
check: async () => 'OK',
})
// Readiness
ekg.addReadinessCheck({
name: 'passing-ready-check',
check: async () => 'OK',
})
const ekgServer = micro(ekg.handler)
ekgServer.listen(3002, () => console.log('listening on port 3002'))
// go to http://localhost:3002/live or http://localhost:3002/ready
API
const EKG = require('@bufferapp/ekg')
// or with all the checks
const {
default: EKG,
httpGetCheck,
dnsResolveCheck,
tcpDialCheck,
mongoDBCheck,
timeoutCheck,
} = require('@bufferapp/ekg')
// or ES6
import EKG, {
httpGetCheck,
dnsResolveCheck,
tcpDialCheck,
mongoDBCheck,
timeoutCheck,
} from '@bufferapp/ekg'
EKG
Construct an EKG instance
const ekg = new EKG()
The ekg instance exposes a few methods:
addLivenessCheck
Add a check to perform when the /live
endpoint is called
// with a custom check
ekg.addLivenessCheck({
name: 'my-new-check',
check: async () => 'OK',
})
// or with a pre-configured check
ekg.addLivenessCheck({
name: 'my-new-check',
check: httpGetCheck({
url: 'http://localhost:3000',
timeout: 5000,
}),
})
addReadinessCheck
Add a check to perform when the /ready
endpoint is called
// with a custom check
ekg.addLivenessCheck({
name: 'my-new-check',
check: async () => 'OK',
})
// or with a pre-configured check
ekg.addLivenessCheck({
name: 'my-new-check',
check: httpGetCheck({
url: 'http://localhost:3000',
timeout: 5000,
}),
})
handler
A function that handles requests and performs readiness and liveness checks
// with micro
micro(ekg.handler)
// or express
app.get('*', async (req, res, next) => {
try {
await ekg.handler(req, res)
} catch (err) {
next(err)
}
})
httpGetCheck
Returns a function that does an HTTP get request on a URL
const doCheck = httpGetCheck({
url: 'http://localhost:3000',
timeout: 5000,
})
doCheck()
dnsResolveCheck
Returns a function does a DNS lookup on a host
const doCheck = dnsResolveCheck({
host: 'buffer.com',
timeout: 5000,
})
doCheck()
tcpDialCheck
Returns a function that creates and connects to a TCP socket
const doCheck = tcpDialCheck({
host: 'buffer.com',
port: 80,
timeout: 5000,
})
doCheck()
mongoDBCheck
Returns a function that pings a mongodb database
const doCheck = mongoDBCheck({
host: 'mongo',
port: 27017,
timeout: 5000,
})
doCheck()
timeoutCheck
Returns a function that runs a function and throws an exception if the function times out
const doCheck = timeoutCheck({
check: () =>
new Promise(resolve => {
// should always fail due to timeout
setTimeout(resolve, 6000)
}),
timeout: 5000,
})
doCheck()