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General

The conventions described in this section are HTTP specific. When HTTP operations occur, metric events about those operations will be generated and reported to provide insight into the operations. By adding HTTP labels to metric events it allows for finely tuned filtering.

Disclaimer: These are initial HTTP metric instruments and labels but more may be added in the future.

Metric Instruments

The following metric instruments MUST be used to describe HTTP operations. They MUST be of the specified type and units.

HTTP Server

Below is a table of HTTP server metric instruments.

Name Instrument Units Description
http.server.duration ValueRecorder milliseconds measures the duration of the inbound HTTP request

HTTP Client

Below is a table of HTTP client metric instruments.

Name Instrument Units Description
http.client.duration ValueRecorder milliseconds measure the duration of the outbound HTTP request

Labels

Below is a table of the labels that SHOULD be included on metric events and whether they should be on server, client, or both types of HTTP metric events:

Name Type Recommended Notes and examples
http.method client & server Yes The HTTP request method. E.g. "GET"
http.host client & server see label alternatives The value of the HTTP host header. When the header is empty or not present, this label should be the same.
http.scheme client & server see label alternatives The URI scheme identifying the used protocol in lowercase: "http" or "https"
http.status_code client & server Optional HTTP response status code. E.g. 200 (String)
http.flavor client & server Optional Kind of HTTP protocol used: "1.0", "1.1", "2", "SPDY" or "QUIC".
net.peer.name client see [1] in label alternatives See general network connection attributes
net.peer.port client see [1] in label alternatives See general network connection attributes
net.peer.ip client see [1] in label alternatives See general network connection attributes
http.server_name server see [2] in label alternatives The primary server name of the matched virtual host. This should be obtained via configuration. If no such configuration can be obtained, this label MUST NOT be set ( net.host.name should be used instead).
net.host.name server see [2] in label alternatives See general network connection attributes
net.host.port server see [2] in label alternatives See general network connection attributes

Parameterized labels

To avoid high cardinality the following labels SHOULD substitute any parameters when added as labels to http metric events as described below:

Label name Type Recommended Notes and examples
http.url client & server see label alternatives The originally requested URL
http.target client & server see label alternatives The full request target as passed in a HTTP request line or equivalent, e.g. "/path/{id}/?q={}".

Many REST APIs encode parameters into the URI path, e.g. /api/users/123 where 123 is a user id, which creates high cardinality value space not suitable for labels on metric events. In case of HTTP servers, these endpoints are often mapped by the server frameworks to more concise HTTP routes, e.g. /api/users/{user_id}, which are recommended as the low cardinality label values. However, the same approach usually does not work for HTTP client labels, especially when instrumentation is provided by a lower-level middleware that is not aware of the specifics of how the URIs are formed. Therefore, HTTP client labels SHOULD be using conservative, low cardinality names formed from the available parameters of an HTTP request, such as "HTTP {METHOD_NAME}". These labels MUST NOT default to using URI path.

Label alternatives

[1] For client metric labels, one of the following sets of labels is RECOMMENDED (in order of usual preference unless for a particular web client/framework it is known that some other set is preferable for some reason; all strings must be non-empty):

  • http.url
  • http.scheme, http.host, http.target
  • http.scheme, net.peer.name, net.peer.port, http.target
  • http.scheme, net.peer.ip, net.peer.port, http.target

[2] For server metric labels, http.url is usually not readily available on the server side but would have to be assembled in a cumbersome and sometimes lossy process from other information (see e.g. open-telemetry/opentelemetry-python#148). It is thus preferred to supply the raw data that is available. Namely, one of the following sets is RECOMMENDED (in order of usual preference unless for a particular web server/framework it is known that some other set is preferable for some reason; all strings must be non-empty):

  • http.scheme, http.host, http.target
  • http.scheme, http.server_name, net.host.port, http.target
  • http.scheme, net.host.name, net.host.port, http.target
  • http.url