A simple and composable HTTP monitoring application written in Go
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A composable monitoring framework written in Go.

It's very alpha and prone to change, so please bear with it. The README is currently outdated as things are in the process of being reorganized.

What is it?

Poller's job is to monitor http applications by submitting GET requests to URL you define in a config file. These URLs are called "Checks".

Once a check is done, the result is sent to one or many backends of your choice.

Current supported backends are stdout, syslog, librato and statsd.

How to configure it

Configuration is done via:

  • Environment variables for backend.
  • JSON for list of checks
  • Flags passed when executing the program.

A typical json file for checks looks like this

        "key": "com_google",                // Key should be unique among all checks specified
        "url": "http://google.com",         // URL of the check
        "interval": "10s",                  // Check will be perfom every 10s. Format available here: http://godoc.org/time#ParseDuration
        "alert": true,                      // (optional) Enable "alerts" for this checks.
        "alertDelay": "60s"                 // (required if alert is set) Wait 60s (or 6 other checks after the first downtime) before sending an alert
        "key": "fr_yahoo",
        "url": "http://yahoo.fr",
        "interval": "10s"
        "key": "connect_sensiolabs_com_api",
        "url": "https://connect.sensiolabs.com/api/",
        "interval": "60s",
        "headers": {
            "Accept": "application/vnd.com.sensiolabs.connect+xml"  // (optional) Added HTTP header

The JSON config file is optional as checks can be added thanks to the HTTP endpoint /checks.

Running ./poller --help will prints a list of available options.

How to monitor it?

A /health http endpoint is available. If poller is answering a 200, then all is good!

How to receive alerts when a check is down?

Alerting and alerting delay is customisable for each check (Please read the example configuration). "Alerters" are enabled from the command line with the --alerts flag.

# Enable the smtp alerter
./poller --alerts="smtp"

# Enable both the pagerduty and smtp alerter
./poller --alerts="smtp,pagerduty"

SMTP Alerter

The SMTP Alerter is enabled when you run poller like this:

./poller --alerts="smtp"

SMTP alerter is configured using these environment variables:

  • SMTP_HOST: (required) ie: localhost
  • SMTP_PORT: (required) ie: 25
  • SMTP_AUTH: (optional) "MD5" or "PLAIN"
  • SMTP_USERNAME: (optional)
  • SMTP_PASSWORD: (optional)
  • SMTP_PLAIN_IDENTITY: (optional)
  • SMTP_RECIPIENT: (required) ie: monitoring@example.org
  • SMTP_FROM: (required) ie: poller@example.org

PagerDuty Alerter

The PagerDuty alerter is enabled when you run poller like this:

./poller --alerts="pagerduty"

PagerDuty's alerter is configured using these environment variables:

How to add checks while poller is running

Poller supports live configuration changes thanks to the /checks http endpoint. Send a PUT request with a valid config JSON in the body of the request and poller will append the checks to its list.

Backends configuration

Here is a list of supported backend and how to configure them with environment variables. Backends are enabled from the command-line thanks to the --backend flag.

# Enable the stdout backend
./poller --backends="stdout"

# Enable both the librato and stdout backend
./poller --backends="librato,stdout"


  • LIBRATO_USER (required): Username of your librato account
  • LIBRATO_TOKEN (required): API token of your librato account
  • LIBRATO_SOURCE (optional): Source name for your metrics. Defaults to poller
  • LIBRATO_PREFIX (optional): Prefix of your metrics. Defaults to poller.checks.

Given your check's key is foobar and LIBRATO_PREFIX is acme.:

On success:

  • 1 will be sent to metrics acme.foobar.up
  • The duration in milliseconds will be sent to foobar.duration

On error or timeout:

  • 0 will be sent to metrics acme.foobar.up
  • The duration in milliseconds will be sent to foobar.duration


No configuration is necessary. Output will look like this:

2012/01/24 11:35:16 com_google UP 345.271ms
2012/01/24 11:35:17 fr_yahoo DOWN 1.518175s
2012/01/24 11:35:17 fr_yahoo ALERT Down since 2006-01-02 15:04:05.999999999 -0700 MST


Statsd backend uses of these environment variables:

  • STATSD_HOST (required): Host of your statsd instance
  • STATSD_PORT (optional): Port of your statsd instance. Defaults to 8125.
  • STATSD_PROTOCOL (optional): Either tcp or udp. Defaults to udp.
  • STATSD_PREFIX (optional): Prefix of your metrics. Defaults to poller.checks.

The metrics are sent the same way as the Librato backend.


You can configure the syslog backend with these:

  • SYSLOG_NETWORK (optional): "tcp", "tcp4" (IPv4-only), "tcp6" (IPv6-only), "udp", "udp4" (IPv4-only), "udp6" (IPv6-only), "ip", "ip4" (IPv4-only), "ip6" (IPv6-only), "unix" and "unixpacket". Defaults to nothing.
  • SYSLOG_ADDRESS (optional): Address of your syslog daemon. Defaults to nothing.
  • SYSLOG_PREFIX (optional): This will be added to your log. Defaults to "poller".

Yes, you can send checks results to loggly by using the syslog backend.

Output formatting is the same as the stdout backend.

Technical documentation

Poller's documentation is available on godoc: http://godoc.org/github.com/marcw/poller

Why Go?

A Go application has the advantage of being concurrent, fast, cross-compilable and easily deployable. I think that's a lot of good reasons to create a monitoring system out of this language.

Install go

note: OSX users, do NOT install Go from homebrew. At time of writing, the package is broken and won't let you cross-compile.

Please follow instructions from: http://golang.org/doc/install/source

Please set a $GOROOT env var in your ~/.bashrc. file. If you unpacked the go source in /home/you/go:

export GOROOT=/home/you/go

Please also set a $GOPATH env var in your ~/.bashrc file. $GOPATH is where go will look for packages and where you clone private projects. An example of $GOPATH would be /home/you/work/go.

export GOPATH=/home/you/work/go

Enable cross compilation with Go

Follow this really good blogpost: http://dave.cheney.net/2012/09/08/an-introduction-to-cross-compilation-with-go


The Poller code is free to use and distribute, under the MIT license.

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