Safe Haskell	None

System.Remote.Monitoring

Contents

Required configuration
Security considerations
REST API
The monitoring server
User-defined counters, gauges, and labels

Description

This module provides remote monitoring of a running process over HTTP. It can be used to run an HTTP server that provides both a web-based user interface and a machine-readable API (e.g. JSON.) The former can be used by a human to get an overview of what the program is doing and the latter can be used by automated monitoring tools.

Typical usage is to start the monitoring server at program startup

 main = do
     forkServer "localhost" 8000
     ...

and then periodically check the stats using a web browser or a command line tool (e.g. curl)

 $ curl -H "Accept: application/json" http://localhost:8000/

Synopsis

Required configuration

To use this module you must first enable GC statistics collection in the run-time system. To enable GC statistics collection, either run your program with

 +RTS -T

or compile it with

 -with-rtsopts=-T

The runtime overhead of -T is very small so it's safe to always leave it enabled.

Security considerations

Be aware that if the server started by forkServer is not bound to "localhost" (or equivalent) anyone on the network can access the monitoring server. Either make sure the network is secure or bind the server to "localhost".

REST API

To use the machine-readable REST API, send an HTTP GET request to the host and port passed to forkServer. The following resources (i.e. URLs) are available:

/: JSON object containing all counters, gauges and labels. Counters, gauges, and labels are stored as nested objects under the counters, gauges, and labels attributes, respectively. Content types: "text/html" (default), "application/json"
/combined: Flattened JSON object containing all counters, gauges, and labels. Content types: "application/json"
/counters: JSON object containing all counters. Content types: "application/json"
/counters/<counter name>: Value of a single counter, as a string. The name should be UTF-8 encoded. Content types: "text/plain"
/gauges: JSON object containing all gauges. Content types: "application/json"
/gauges/<gauge name>: Value of a single gauge, as a string. The name should be UTF-8 encoded. Content types: "text/plain"
/labels: JSON object containing all labels. Content types: "application/json"
/labels/<label name>: Value of a single label, as a string. The name should be UTF-8 encoded. Content types: "text/plain"

Counters, gauges and labels are stored as attributes of the returned JSON objects, one attribute per counter, gauge or label. In addition to user-defined counters, gauges, and labels, the below built-in counters and gauges are also returned. Furthermore, the top-level JSON object of any resource contains the server_timestamp_millis attribute, which indicates the server time, in milliseconds, when the sample was taken.

Built-in counters:

bytes_allocated: Total number of bytes allocated
num_gcs: Number of garbage collections performed
num_bytes_usage_samples: Number of byte usage samples taken
cumulative_bytes_used: Sum of all byte usage samples, can be used with numByteUsageSamples to calculate averages with arbitrary weighting (if you are sampling this record multiple times).
bytes_copied: Number of bytes copied during GC
mutator_cpu_seconds: CPU time spent running mutator threads. This does not include any profiling overhead or initialization.
mutator_wall_seconds: Wall clock time spent running mutator threads. This does not include initialization.
gc_cpu_seconds: CPU time spent running GC
gc_wall_seconds: Wall clock time spent running GC
cpu_seconds: Total CPU time elapsed since program start
wall_seconds: Total wall clock time elapsed since start

Built-in gauges:

max_bytes_used: Maximum number of live bytes seen so far
current_bytes_used: Current number of live bytes
current_bytes_slop: Current number of bytes lost to slop
max_bytes_slop: Maximum number of bytes lost to slop at any one time so far
peak_megabytes_allocated: Maximum number of megabytes allocated
par_tot_bytes_copied: Number of bytes copied during GC, minus space held by mutable lists held by the capabilities. Can be used with parMaxBytesCopied to determine how well parallel GC utilized all cores.
par_avg_bytes_copied: Deprecated alias for par_tot_bytes_copied.
par_max_bytes_copied: Sum of number of bytes copied each GC by the most active GC thread each GC. The ratio of par_tot_bytes_copied divided by par_max_bytes_copied approaches 1 for a maximally sequential run and approaches the number of threads (set by the RTS flag -N) for a maximally parallel run.

The monitoring server

data Server Source

A handle that can be used to control the monitoring server. Created by forkServer.

serverThreadId :: Server -> ThreadId Source

The thread ID of the server. You can kill the server by killing this thread (i.e. by throwing it an asynchronous exception.)

forkServer Source

Arguments

:: ByteString	Host to listen on (e.g. "localhost")
-> Int	Port to listen on (e.g. 8000)
-> IO Server

Start an HTTP server in a new thread. The server replies to GET requests to the given host and port. The host argument can be either a numeric network address (dotted quad for IPv4, colon-separated hex for IPv6) or a hostname (e.g. "localhost".) The client can control the Content-Type used in responses by setting the Accept header. At the moment three content types are available: "application/json", "text/html", and "text/plain".

User-defined counters, gauges, and labels

The monitoring server can store and serve user-defined, integer-valued counters and gauges, and string-valued labels. A counter is a monotonically increasing value (e.g. TCP connections established since program start.) A gauge is a variable value (e.g. the current number of concurrent connections.) A label is a free-form string value (e.g. exporting the command line arguments or host name.) Each counter, gauge, and label is associated with a name, which is used when it is displayed in the UI or returned in a JSON object.

Even though it's technically possible to have a counter and a gauge with the same name, associated with the same server, it's not recommended as it might make it harder for clients to distinguish the two.

To create and use a counter, simply call getCounter to create it and then call e.g. inc or add to modify its value. Example:

 main = do
     handle <- forkServer "localhost" 8000
     counter <- getCounter "iterations" handle
     let loop n = do
             inc counter
             loop
     loop

To create a gauge, use getGauge instead of getCounter and then call e.g. set or modify. Similar for labels.

getCounter Source

Arguments

:: Text	Counter name
-> Server	Server that will serve the counter
-> IO Counter

Return the counter associated with the given name and server. Multiple calls to getCounter with the same arguments will return the same counter. The first time getCounter is called for a given name and server, a new, zero-initialized counter will be returned.

getGauge Source

Arguments

:: Text	Gauge name
-> Server	Server that will serve the gauge
-> IO Gauge

Return the gauge associated with the given name and server. Multiple calls to getGauge with the same arguments will return the same gauge. The first time getGauge is called for a given name and server, a new, zero-initialized gauge will be returned.

getLabel Source

Arguments

:: Text	Label name
-> Server	Server that will serve the label
-> IO Label

Return the label associated with the given name and server. Multiple calls to getLabel with the same arguments will return the same label. The first time getLabel is called for a given name and server, a new, empty label will be returned.