Traffic Log

With the Traffic Log policy you can easily set up access logs on every data plane in a mesh.

This policy only records outbound traffic. It doesn’t record inbound traffic.

To configure access logs in Kuma you need to:

In the rest of this page we assume you have already configured your observability tools to work with Kuma. If you haven’t already read the observability docs.

Add a logging backend

A logging backend is essentially a sink for access logs.

Currently, it can be either a file or a TCP log collector, such as Logstash, Splunk or other.

kind: Mesh
  name: default
    # TrafficLog policies may leave the `backend` field undefined.
    # In that case the logs will be forwarded into the `defaultBackend` of that Mesh.
    defaultBackend: file
    # List of logging backends that can be referred to by name
    # from TrafficLog policies of that Mesh.
      - name: logstash
        # Use `format` field to adjust the access log format to your use case.
        format: '{"start_time": "%START_TIME%", "source": "%KUMA_SOURCE_SERVICE%", "destination": "%KUMA_DESTINATION_SERVICE%", "source_address": "%KUMA_SOURCE_ADDRESS_WITHOUT_PORT%", "destination_address": "%UPSTREAM_HOST%", "duration_millis": "%DURATION%", "bytes_received": "%BYTES_RECEIVED%", "bytes_sent": "%BYTES_SENT%"}'
        type: tcp
        # Use `config` field to co configure a TCP logging backend.
          # Address of a log collector (like logstash, splunk or other).
      - name: file
        type: file
        # Use `file` field to configure a file-based logging backend.
          path: /tmp/access.log
        # When `format` field is omitted, the default access log format will be used.

Add a TrafficLog resource

You need to create a TrafficLog policy to select a subset of traffic and write its access logs into one of the backends configured for that mesh.

kind: TrafficLog
  name: all-traffic
mesh: default
  # This TrafficLog policy applies all traffic in that Mesh.
    - match: "*"
    - match: "*"
kind: TrafficLog
  name: backend-to-database-traffic
mesh: default
  # This TrafficLog policy applies only to traffic from service `backend` to service `database`.
    - match: backend_kuma-example_svc_8080
    - match: database_kuma-example_svc_5432
    # Forward the logs into the logging backend named `logstash`.
    backend: logstash

When backend field is omitted, the logs will be forwarded into the defaultBackend of that Mesh.


TrafficLog is an Outbound Connection Policy. For this reason the only supported value for destinations.match is

Logging external services

When running Kuma on Kubernetes you can also log the traffic to external services. To do it, the matched destination section has to have wildcard * value. In such case %KUMA_DESTINATION_SERVICE% will have value external and %UPSTREAM_HOST% will have an IP of the service.

Builtin Gateway support

Traffic Log is a Kuma outbound connection policy, so Kuma chooses a Traffic Log policy by matching the service tag of the data plane’s outbounds. Since a builtin gateway data plane does not have outbounds, Kuma always uses the builtin service name pass_through to match the Traffic Log policy for Gateways.

Access Log Format

Kuma gives you full control over the format of the access logs.

The shape of a single log record is defined by a template string that uses command operators to extract and format data about a TCP connection or an HTTP request.



where %START_TIME% and %KUMA_SOURCE_SERVICE% are examples of available command operators.

All command operators defined by Envoy are supported, along with additional command operators defined by Kuma:

Command Operator Description
%KUMA_MESH% name of the mesh in which traffic is flowing
%KUMA_SOURCE_SERVICE% name of a service that is the source of traffic
%KUMA_DESTINATION_SERVICE% name of a service that is the destination of traffic
%KUMA_SOURCE_ADDRESS_WITHOUT_PORT% address of a Dataplane that is the source of traffic

Access Logs for TCP and HTTP traffic

All access log command operators are valid to use with both TCP and HTTP traffic.

If a command operator is specific to HTTP traffic, such as %REQ(X?Y):Z% or %RESP(X?Y):Z%, it will be replaced by a symbol “-” in case of TCP traffic.

Internally, Kuma determines traffic protocol based on the value of tag on the inbound interface of a destination Dataplane.

The default format string for TCP traffic is:


The default format string for HTTP traffic is:


To provide different format for TCP and HTTP logging you can define two separate logging backends with the same address and different format. Then define two TrafficLog entity, one for TCP and one for HTTP with matching selector.

JSON format

If you need an access log with entries in JSON format, you have to provide a template string that is a valid JSON object, e.g.

  "start_time":          "%START_TIME%",
  "source":              "%KUMA_SOURCE_SERVICE%",
  "destination":         "%KUMA_DESTINATION_SERVICE%",
  "source_address":      "%KUMA_SOURCE_ADDRESS_WITHOUT_PORT%",
  "destination_address": "%UPSTREAM_HOST%",
  "duration_millis":     "%DURATION%",
  "bytes_received":      "%BYTES_RECEIVED%",
  "bytes_sent":          "%BYTES_SENT%"
Last Updated: 11/4/2022, 19:20:08 PM