| Safe Haskell | None |
|---|
System.Remote.Monitoring
Contents
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/
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.
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 and gauges. Counters and
gauges are stored as nested objects under the
countersandgaugesattributes, 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
numByteUsageSamplesto 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
The monitoring server
A handle that can be used to control the monitoring server.
Created by forkServer.
serverThreadId :: Server -> ThreadIdSource
The thread ID of the server. You can kill the server by killing this thread (i.e. by throwing it an asynchronous exception.)
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-value 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.
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.