Ubuntu Manpage: PMWEBAPI - introduction to the Performance Metrics Web Application Programming Interface

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.

       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.

CONTEXT CREATION: configurable permanent contexts

       In addition, permanent contexts may be created by pmwebd at initialization using  its  -h,
       -a, -L command line options, so that a set of fixed NNNNN numbers may be made available to
       web clients.

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.

METRIC METADATA: pmLookupName, pmLookupDesc, pmLookupText, pmTraversePMNS_r
The general form of the requests is as follows:

/pmapi/NNNNN/_metric
Traverse the entire Performance Metrics Name Space (PMNS).

/pmapi/NNNNN/_metric?prefix=NAME
Traverse the subtree of PMNS with the prefix NAME.

The response is a JSON document that provides the metric metadata as an array. For
example:

{ "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", ... }
...
] }

Most of the fields are self-explanatory.

name A name for the metric as defined in the PMNS. If the PMNS contains multiple names
associated with the metric's Performance Metric Identifier (PMID), one of these
will be returned via name, but there is no way to determine which of the duplicate
names this will be.

PPPP the PMID

DDDD the instance domain

type from pmTypeStr

units from pmUnitsStr

sem an abbreviation of the metric semantic:

PM_SEM_COUNTER "counter"
PM_SEM_INSTANT "instant"
PM_SEM_DISCRETE "discrete"

METRIC VALUE: pmFetch
The general form of the requests is as follows:

/pmapi/NNNNN/_fetch?names=NAME1,NAME2
Fetch current values for given named metrics.

/pmapi/NNNNN/_fetch?pmids=PPPP1,PPPP2
Fetch current values for given PMIDs.

If any of the names/pmids are valid, the response is a JSON document that provides the
values for all requested metrics, for all their instances.

{ "timestamp": { "s":SEC, "us":USEC },
"values": [
{ "pmid":PPPP1, "name":"NAME1",
"instances:" [
{ "instance":IIII1, "value":VALUE1 }
{ "instance":IIII2, "value":VALUE2 }
...
] },
{ "pmid":PPPP2, "name":"NAME2", ... }
...
] }

Most of the fields are self-explanatory. Numeric metric types are represented as JSON
integer or floating-point values. Strings are passed verbatim, except that non-ASCII
values are replaced with a Unicode 0xFFFD REPLACEMENT CHARACTER code. Event type metrics
are not currently supported.

INSTANCE DOMAINS METADATA: pmGetInDom, pmNameInDom, pmLookupInDom
The general form of the requests is as follows:

/pmapi/NNNN/_indom?indom=DDDD
List instances of the given instance domain.

/pmapi/NNNN/_indom?name=NAME
List instances of the instance domain belonging to the named metric.

In addition, either query may be suffixed with:

&instance=IIII,JJJJ
Restrict listings to given instance code numbers.

&iname=INAME1,INAME2
Restrict listings to given instance names.

The response is a JSON document that provides the metric metadata as an array. For
example:

{ "indom":DDDD,
"instances": [
{ "instance":IIII, "name":"INAME" }
...
] }

INSTANCE PROFILE: pmAddProfile, pmDelProfile
The general form of these requests is as follows:

/pmapi/NNNN/_profile_reset?indom=DDDD
These are not currently supported.

/pmapi/NNNN/_profile_add?indom=DDDD&instance=IIII,JJJJ
These are not currently supported.

/pmapi/NNNN/_profile_add?indom=DDDD&iname=IIII,JJJJ
These are not currently supported.

/pmapi/NNNN/_profile_del?indom=DDDD&instance=JJJJ
These are not currently supported.

/pmapi/NNNN/_profile_del?indom=DDDD&iname=INAME1,INAME2
These are not currently supported.

METRIC STORE: pmStore
The general form of these requests is as follows:

/pmapi/NNNN/_store?name=NAME&value=VALUE
Store a new value for given named metrics.

/pmapi/NNNNN/_store?pmid=PPPP&value=VALUE
Store a new value for given performance metric identifier (PMID).

In addition, either query may be suffixed with:

&instance=IIII,JJJJ
Restrict store to given instance code numbers.

&iname=INAME1,INAME2
Restrict store to given instance names.

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

{ "success" : true }

DERIVED METRICS: pmRegisterDerived
/pmapi/NNNNN/_derive?name=NAME&expr=EXPRESSION
These are not currently supported.

CONTEXT COPY: pmDupContext
/pmapi/NNNNN/copy
These are not currently supported.

CONTEXT CLOSE: pmDestroyContext
/pmapi/NNNNN/destroy
This is not likely to be supported, as it is destructive and would offer a tempting
target to brute-force attackers. Instead, the pmwebd timeout is used to
automatically free unused contexts.

PROMETHEUS
Prometheus exporting of live metrics from a preexisting PMWEBAPI context is available:

The general form of the requests is:

/pmapi/NNNNN/metrics?target=NAME1,NAME2,...
Fetch current values for given named metrics.

For all numeric metrics with the given NAME prefixes, create a prometheus text export
format giving their current value and related metadata. The response has text/plain type
rather than JSON, and is designed to be ingested by a Prometheus server, or pcp's own
pmdaprometheus.

The native PCP metric metadata (metric name, semantics and units) are first output with
the # PCP prefix. If the units string is empty, then none is output. The units metadata
string may contain spaces and extends to the end of the line. Prometheus metric types are
heuristically inferred from PCP metric types, and units/scales are converted to base
seconds/bytes/count if possible, with a corresponding suffix added to the metric name.
PCP metric names are mapped so that . are exchanged with :. Instance domain instances are
represented as Prometheus labels with quoted instance names.

# PCP proc.nprocs instant none
# HELP proc:nprocs instantaneous number of processes
# TYPE proc:nprocs gauge
proc:nprocs 7

# PCP kernel.pernode.cpu.intr counter millisec
# HELP kernel:pernode:cpu:intr_seconds_total total interrupt CPU time from /proc/stat for each node
# TYPE kernel:pernode:cpu:intr_seconds_total counter
kernel:pernode:cpu:intr_seconds_total{instance="node0"} 25603.540000000001

# PCP filesys.blocksize instant byte
# HELP filesys:blocksize_bytes Size of each block on mounted filesystem (Bytes)
# TYPE filesys:blocksize_bytes gauge
filesys:blocksize_bytes{instance="/dev/mapper/docker-253:0-83713-\
9a130460b46163fcf4443710db3159dea6bb5ec2aaca108515839a7a28c191ce"} 4096
filesys:blocksize_bytes{instance="/dev/mapper/VolGroup00-root17"} 4096

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