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Metrics, logs and telemetry

Status endpoint

Imposter exposes a status endpoint under /system/status

This is useful as a healthcheck endpoint, such as for liveness or readiness checks.

$ curl http://localhost:8080/system/status



Imposter exposes telemetry using Prometheus under /system/metrics

This enables you to examine track various metrics, such as response time, error rates, total request count etc.

$ curl http://localhost:8080/system/metrics

# HELP vertx_http_server_bytesReceived Number of bytes received by the server
# TYPE vertx_http_server_bytesReceived summary
vertx_http_server_bytesReceived_count 6.0

# HELP vertx_http_server_requestCount_total Number of processed requests
# TYPE vertx_http_server_requestCount_total counter
vertx_http_server_requestCount_total{code="200",method="GET",} 5.0

# HELP vertx_http_server_connections Number of opened connections to the server
# TYPE vertx_http_server_connections gauge
vertx_http_server_connections 2.0

# HELP vertx_http_server_responseTime_seconds Request processing time
# TYPE vertx_http_server_responseTime_seconds summary
vertx_http_server_responseTime_seconds_count{code="200",method="GET",} 5.0
vertx_http_server_responseTime_seconds_sum{code="200",method="GET",} 0.1405811

# HELP vertx_http_server_responseTime_seconds_max Request processing time
# TYPE vertx_http_server_responseTime_seconds_max gauge
vertx_http_server_responseTime_seconds_max{code="200",method="GET",} 0.1039024

For example, to calculate the average response time, use the following PromQL:

vertx_http_server_responseTime_seconds_sum / vertx_http_server_responseTime_seconds_count

Other useful metrics:

Metric name Purpose
response_file_cache_entries The number of cached response files
script_execution_duration Script engine execution duration in seconds
script_cache_entries The number of cached compiled scripts

Also see the metrics example.


Logs are printed to stdout.

You can control the logging level using the following environment variable:

# also supports WARN, INFO, DEBUG etc.

Internally, Log4J2 is used, so the usual configuration options apply.

Structured logging

Imposter can log a JSON summary of each request, such as the following:

  "timestamp" : "2021-12-16T22:13:24.999Z",
  "uri" : "http://localhost:8080/pets/1",
  "path" : "/pets/1",
  "method" : "GET",
  "statusCode" : "200",
  "scriptTime" : "30.80",
  "duration" : "34.49"

To enable this, set the environment variable IMPOSTER_LOG_SUMMARY=true.

Logging request/response headers

You can optionally include request and response headers in the JSON summary such as:

  "timestamp" : "2021-12-16T22:13:24.999Z",
  "uri" : "http://localhost:8080/pets/1",
  "path" : "/pets/1",
  "method" : "GET",
  "statusCode" : "200",
  "scriptTime" : "350.80",
  "duration" : "374.49",
  "x-correlation-id" : "aabbcc12345",
  "user-agent" : "Mozilla/5.0 (platform; rv:17.0) Gecko/geckotrail Firefox/90",
  "content-length" : "123"

Note the presence of x-correlation, user-agent and content-length fields.

To add these, set the following environment variables:


Logging request/response body

You can optionally include the request and/or response body in the JSON summary.

To enable these, set the following environment variables: