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System.Net metrics

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This article describes the networking metrics built-in for System.Net produced using the System.Diagnostics.Metrics API. For a listing of metrics based on the alternate EventCounters API, see Well-known EventCounters in .NET.

Tip

For more information about how to collect, report, enrich, and test System.Net metrics, see Networking metrics in .NET.

System.Net.NameResolution

The System.Net.NameResolution metrics report DNS name resolution from Dns:

Metric: dns.lookup.duration
Name Instrument Type Unit Description
dns.lookup.duration Histogram s Measures the time taken to perform a DNS lookup.
Attribute Type Description Examples Presence
dns.question.name string The name being queried. www.example.com; dot.net Always
error.type string A well-known error string or the full type name of an exception that occurred. host_not_found; System.Net.Sockets.SocketException If an error occurred

This metric measures the time take to make DNS requests. These requests can occur by calling methods on Dns or indirectly within higher level APIs on types such as HttpClient.

Most errors when doing a DNS lookup throw a SocketException. To better disambiguate the common error cases, socket exceptions with specific SocketErrorCode are given explicit error names in error.type:

SocketErrorCode error.type
HostNotFound host_not_found
TryAgain try_again
AddressFamilyNotSupported address_family_not_supported
NoRecovery no_recovery

Socket exceptions with any other SocketError value are reported as System.Net.Sockets.SocketException.

When using OpenTelemetry, the default buckets for this metric are set to [ 0.005, 0.01, 0.025, 0.05, 0.075, 0.1, 0.25, 0.5, 0.75, 1, 2.5, 5, 7.5, 10 ].

Available starting in: .NET 8

System.Net.Http

The System.Net.Http metrics report HTTP request and connection information from System.Net.Http:

Metric: http.client.open_connections
Name Instrument Type Unit (UCUM) Description
http.client.open_connections UpDownCounter {connection} Number of outbound HTTP connections that are currently active or idle on the client
Attribute Type Description Examples Presence
http.connection.state string State of HTTP connection in the HTTP connection pool. active; idle Always
network.protocol.version string Version of the HTTP protocol used. 1.1; 2 Always
server.address string Host identifier of the "URI origin" HTTP request is sent to. example.com Always
server.port int Port identifier of the "URI origin" HTTP request is sent to. 80; 8080; 443 If not default (80 for http scheme, 443 for https)
network.peer.address string Peer IP address of the socket connection. 10.5.3.2 Always
url.scheme string The URI scheme component identifying the used protocol. http; https; ftp Always

HttpClient, when configured to use the default SocketsHttpHandler, maintains a cached pool of network connections for sending HTTP messages. This metric counts how many connections are currently in the pool. Active connections are handling active requests. Active connects could be transmitting data or awaiting the client or server. Idle connections aren't handling any requests, but are left open so that future requests can be handled more quickly.

Available starting in: .NET 8

Metric: http.client.connection.duration
Name Instrument Type Unit (UCUM) Description
http.client.connection.duration Histogram s The duration of successfully established outbound HTTP connections.
Attribute Type Description Examples Presence
network.protocol.version string Version of the HTTP protocol used. 1.1; 2 Always
server.address string Host identifier of the "URI origin" HTTP request is sent to. example.com Always
server.port int Port identifier of the "URI origin" HTTP request is sent to. 80; 8080; 443 If not default (80 for http scheme, 443 for https)
network.peer.address string IP address of the socket connection. 10.5.3.2 Always
url.scheme string The URI scheme component identifying the used protocol. http; https; ftp Always

This metric is only captured when HttpClient is configured to use the default SocketsHttpHandler.

As this metric is tracking the connection duration, and ideally http connections are used for multiple requests, the buckets should be longer than those used for request durations. For example, using [ 0.01, 0.02, 0.05, 0.1, 0.2, 0.5, 1, 2, 5, 10, 30, 60, 120, 300 ] provides an upper bucket of 5 mins.

Available starting in: .NET 8

Metric: http.client.request.duration
Name Instrument Type Unit (UCUM) Description
http.client.request.duration Histogram s The duration of outbound HTTP requests.
Attribute Type Description Examples Presence
error.type string Request failure reason: one of the HTTP request errors in snake_case, or a full exception type, or an HTTP 4xx/5xx status code. System.Threading.Tasks.TaskCanceledException; name_resolution_error; secure_connection_error ; 404 If request has failed.
http.request.method string HTTP request method. GET; POST; HEAD; _OTHER [2] Always
http.response.status_code int HTTP response status code. 200 If response was received.
network.protocol.version string Version of the HTTP protocol used. 1.1; 2 If response was received.
server.address string Host identifier of the "URI origin" HTTP request is sent to. example.com Always
server.port int Port identifier of the "URI origin" HTTP request is sent to. 80; 8080; 443 Depends on .NET version. [3]
url.scheme string The URI scheme component identifying the used protocol. http; https; ftp Always

[1] error.type: If the request has failed, the value is set to one of the following:

  • An exception name with type, for example, TaskCanceledException.
  • A status code that indicates a client or server error, for example, 500.
  • If an HttpRequestException occurred with an HttpRequestError other than Unknown, the enum value in snake case, for example, name_resolution_error.

[2] http.request.method: http.request.method:** The value contains the method name, if the method is one of the well-known methods listed in RFC9110; otherwise the value is _OTHER. The user-provided method names will be mapped to known names in a case-insensitive manner. For example, if the user provides the name GeT, it will be mapped to GET.

[3] server.port: The Presence of the value is version-dependent:

  • .NET 8: Present if not default (80 for http scheme, 443 for https)
  • .NET 9+: Always present

HTTP client request duration measures the time the underlying client handler takes to complete the request. Completing the request includes the time up to reading response headers from the network stream. It doesn't include the time spent reading the response body.

When using OpenTelemetry, the default buckets for this metric are set to [ 0.005, 0.01, 0.025, 0.05, 0.075, 0.1, 0.25, 0.5, 0.75, 1, 2.5, 5, 7.5, 10 ].

Available starting in: .NET 8

Tip

Enrichment is possible for this metric.

Metric: http.client.request.time_in_queue
Name Instrument Type Unit (UCUM) Description
http.client.request.time_in_queue Histogram s The amount of time requests spent on a queue waiting for an available connection.
Attribute Type Description Examples Presence
http.request.method string HTTP request method. GET; POST; HEAD Always
network.protocol.version string Version of the HTTP protocol used. 1.1; 2 Always
server.address string Host identifier of the "URI origin" HTTP request is sent to. example.com Always
server.port int Port identifier of the "URI origin" HTTP request is sent to. 80; 8080; 443 If not default (80 for http scheme, 443 for https)
url.scheme string The URI scheme component identifying the used protocol. http; https; ftp Always

HttpClient, when configured to use the default SocketsHttpHandler, sends HTTP requests using a pool of network connections. If all connections are busy handling other requests, new requests are placed in a queue and wait until a network connection is available for use. This instrument measures the amount of time HTTP requests spend waiting in that queue, prior to anything being sent across the network.

Available starting in: .NET 8

Metric: http.client.active_requests
Name Instrument Type Unit (UCUM) Description
http.client.active_requests UpDownCounter {request} Number of active HTTP requests.
Attribute Type Description Examples Presence
http.request.method string HTTP request method. GET; POST; HEAD Always
server.address string Host identifier of the "URI origin" HTTP request is sent to. example.com Always
server.port int Port identifier of the "URI origin" HTTP request is sent to. 80; 8080; 443 If not default (80 for http scheme, 443 for https)
url.scheme string The URI scheme component identifying the used protocol. http; https; ftp Always

This metric counts how many requests are considered active. Requests are active for the same time period that is measured by the http.client.request.duration instrument.

Available starting in: .NET 8