NAME¶

PMWEBAPI - introduction to the Performance Metrics Web Application Programming Interface

OVERVIEW¶

The PMWEBAPI interface is a binding of a subset of the PMAPI to the web. It uses HTTP as transport, REST as organizational style for request/parameter encoding (the GET and POST methods are interchangeable), and JSON as response encoding. A context identifier is used as a persistent way to refer to PMAPI contexts across related web requests. These context identifiers expire after a configurable period of disuse.

Errors generally result in HTTP-level error responses. An Access-Control-Allow-Origin: * header is added to all JSON responses.

CONTEXT CREATION: pmNewContext¶

To create a new web context identifier, a web client invokes:

/pmapi/context?hostname=STRING

/pmapi/context?hostspec=STRING

Creates a PM_CONTEXT_HOST PMAPI context with the given host name and/or extended specification. If the host specification contains a userid/password combination, then the corresponding PMAPI context operations will require HTTP Basic authentication credentials with matching userid/password.

/pmapi/context?archivefile=ARCHIVE

Creates a PM_CONTEXT_ARCHIVE PMAPI context with the given file name. Only metrics from the given archive are available.

In addition, the web client may add the parameter &polltimeout=MMMM for a maximum interval (in seconds) between expected accesses to the given context. This value is limited by pmwebd configuration, and is a courtesy to allow pmwebd to free up memory earlier in case of sudden web application shutdown.

If successful, the response from these requests is a JSON document of the form:

{ "context" : NNNNN }

The number (a 32-bit unsigned decimal) is then used in all later operations.

PMAPI OPERATIONS¶

The general form of the requests is as follows: /pmapi/NNNNN/OPERATION where

/pmapi

is the fixed prefix for all PMWEBAPI operations,

NNNNN

is a PMWEBAPI context number returned from a context-creation call, or assigned permanently at pmwebd startup, and

OPERATION?PARAM1=VALUE2&PARAM2=VALUE2

identifies the operation and its URL-encoded parameters. Some parameters may be optional.

{ "metrics": [ 


    { "name":"foo.bar", "pmID":PPPP, "indom":DDDD,


      "type":"32", "sem":"instant", "units":"MHz",


      "text-oneline":"foo bar", "text-help":"blah blah blah" },


    { "name":"foo.bar2", ... }


    ...


  ] }

{ "timestamp": { "s":SEC, "us":USEC },


  "values": [


        { "pmid":PPPP1, "name":"NAME1",


          "instances:" [


               { "instance":IIII1, "value":VALUE1 }


               { "instance":IIII2, "value":VALUE2 }


               ...


          ] },


        { "pmid":PPPP2, "name":"NAME2", ... }


        ...


  ] }

{ "indom":DDDD,


   "instances": [


      { "instance":IIII, "name":"INAME" }


      ...


   ] }

{ "success" : true }

GRAPHITE¶

When enabled, pmwebd can emulate a subset of the graphite web-api to allow web applications like graphite and grafana to extract data from all archives under the configured -A directory. The graphite namespace is constructed from the PCP archives using a simple mapping that encodes the Cartesian product of archives, metrics, and instance-domain instances into dot-separated strings. Some metacharacter-quoting is employed to encode general strings into components. Only numeric PCP metrics are exposed; COUNTER semantic values are rate-converted.

Since glob wildcarding is supported within metric name components, using them in the first component (an encoding of the archive name) is a good way to identify machines, or to match multiple archives spanning times of interest. Compressed archives are excluded.

We list here only the broadest outline of the supported calls. pmwebd does not support every graphite web-api option, so many querystring parameters may be ignored. Arithmetic/statistical functions on metrics are not supported.

/graphite/render&format=json&target=FOO&from=TIME&until=TIME

Return a series of values of the given metrics, between the two times, sampled every 60 seconds.

/graphite/rawdata&target=FOO.BAR&from=TIME&until=TIME

Same, with a slightly different result encoding.

/graphite/render&format=png&target=FOO&from=TIME&until=TIME&....

Same, but render the curves into a PNG image file. Several color- and rendering-control-related parameters are supported.

/graphite/metrics/find&query=FOO.BAR.*

Provide incremental metric-tree traversal uwing wildcards.

/graphite/graphlot/findmetric&query=FOO+BAR

Search through metrics with space-separated regular expressions.

/graphite/browser/search&q=FOO+BAR

Same, with a slightly different result encoding.

SEE ALSO¶

PCPIntro(1), PCPIntro(3), pmwebd(1), http://graphite.readthedocs.org/ and PMAPI(3)