Why & When

This is a Spring Boot 2 Starter exposing the JDK Flight Recorder as a Spring Boot Actuator Endpoint.

Normally the JDK Flight Recorder is available locally or by JMX remote. Depending on your deployment scenario shell or JMX access might not be available for the application server. Here comes this handy starter into play!

How

This starter adds a new Spring Boot Actuator endpoint for JDK Flight Recorder remote control. This RESTful endpoint allows starting and stopping Flight Recording and downloading the .jfr files for further analysis.

Spring Boot 2

Just add the following dependency to your Spring Boot 2 project:

<dependency>
    <groupId>de.mirkosertic</groupId>
    <artifactId>flight-recorder-starter</artifactId>
    <version>2.3.1</version>
</dependency>

Spring Boot 3

Just add the following dependency to your Spring Boot 3 project:

<dependency>
    <groupId>de.mirkosertic</groupId>
    <artifactId>flight-recorder-starter</artifactId>
    <version>3.1.0</version>
</dependency>

Required for all Spring Boot versions

Please don't forget to add the following configuration:

flightrecorder:
  enabled: true  # is this starter active?

IMPORTANT: By default, this starter doesn't include spring webmvc or spring webflux dependencies. You will have to include them according the stack you wish.

WebMvc

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-web</artifactId>
</dependency>

WebFlux

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-webflux</artifactId>
</dependency>

Please note: the minimum Java/JVM runtime version is 11!

Starting Flight Recording

The following cURL command starts a new Flight Recording and returns the created Flight Recording ID:

curl  -i -X POST -H "Content-Type: application/json" -d '{"duration": "60","timeUnit":"SECONDS"}' http://localhost:8080/actuator/flightrecorder/

HTTP/1.1 201 
Location: http://localhost:8080/actuator/flightrecorder/1
Content-Length: 0
Date: Fri, 05 Feb 2021 12:37:07 GMT

Flight Recording starts for a given period, in this case 60 seconds and stops then.

Every recording session gets its own unique Flight Recording ID. The endpoint returns this ID as plain text, in this case ID 1. This ID must be used to download the recorded data.

Advanced commands

In order to cover more recording options, the payload sent can be composed by different params. Following the whole list of params:

Field Key	Value Type	Mandatory	Description
description	String	NO	The description for the recording
duration	Number	YES	The duration of recording
timeUnit	Serialized ChronoUnit value	YES	The unit for duration param
maxAgeDuration	Number	NO	The max age of data you can preserve
maxAgeUnit	Serialized ChronoUnit value	NO	The unit for maxAge param
delayDuration	Number	NO	Schedule the recording
delayUnit	Serialized ChronoUnit value	NO	The unit for delay param
maxSize	Number	NO	Max size of file (in bytes)
customSettings	JSON Object with N fields	NO	JSON object with custom properties that will override the properties in the base configuration

More info at JFR Javadoc here.

Example of JSON param:

{
  "description": "MyFirstRecording",
  "duration": "60",
  "timeUnit": "SECONDS",
  "maxAgeDuration": "10",
  "maxAgeUnit": "SECONDS",
  "delayDuration": "5",
  "delayUnit": "SECONDS",
  "maxSize": "100000",
  "customSettings": {
    "myCustomProperty1": "myCustomValue1",
    "myCustomProperty2": "myCustomValue2"
  }
}

Downloading results

The following cURL command stops the Flight Recording with ID 1 and downloads the .jfr file:

curl --output recording.jfr http://localhost:8080/actuator/flightrecorder/1

The downloaded .jfr file can be imported into JDK Mission Control (JMC) for further analysis.

Visiting the interactive Flamegraph

This starter can generate an interactive Flamegraph from a Flight Recorder recording. You can gain a quick overview by visiting the following URL in your browser to see the graph for a recording with ID 1:

http://localhost:8080/actuator/flightrecorder/ui/1/flamegraph.html

and you'll get:

The starter automatically tries to visualize only classes belonging to the running Spring Boot application. It filters the stacktrace samples by classes that are in the package or sub-package of the running application instance annotated with a @SpringBootApplication annotation.

However, you can always get the unfiltered Flamegraph by visiting:

http://localhost:8080/actuator/flightrecorder/ui/1/rawflamegraph.html

Stopping Flight Recording

The following cURL command stops the Flight Recording with ID 1.

curl -i -X PUT http://localhost:8080/actuator/flightrecorder/1


HTTP/1.1 200
Content-Type: application/json
Transfer-Encoding: chunked
Date: Fri, 05 Feb 2021 12:39:43 GMT

{"id":1,"startedAt":"2021-02-05 13:37:08","status":"CLOSED","finishedAt":"2021-02-05 13:39:43","description":null}

Delete Flight Recording

The following cURL command stops the Flight Recording with ID 1.

curl -i -X DELETE http://localhost:8080/actuator/flightrecorder/1

HTTP/1.1 204 
Date: Fri, 05 Feb 2021 12:40:13 GMT

Later, this recording might be deleted in memory and physically by the scheduler process described below.

Auto-deletion process

IMPORTANT: Be aware that the main app should be annotated with @EnableScheduling to enable the scheduled processes for auto-deletion.

The process periodically deletes recording files, which are in status STOPPED or CLOSED. The cleanup interval can be configured via

flightrecorder.recording-cleanup-interval=5000

with default value set on 5000ms. The base unit is MILLISECONDS. Take into account that the deletion is permanently.

The watermark used to annotate a recording as "removable" is either time-based (TTL) or count-based (COUNT).

The default cleanup type is TTL and can be changed using the property:

flightrecorder.recording-cleanup-type=COUNT

Deletion by TTL

If the cleanup type is TTL (time to live), the recording's start time represents the reference point for the TTL deletion. The threshold can be configured via the properties below (default: 1 Hour):

flightrecorder.old-recordings-TTL=1
flightrecorder.old-recordings-TTL-time-unit=Hours  # java.time.temporal.ChronoUnit available values

A file will be removed when the status is STOPPED or CLOSED, and the recording's start time is before now minus threshold configured.

Deletion by COUNT

If the cleanup type is COUNT, the oldest recordings will be deleted when the total number of existing recordings surpasses the configured threshold of recordings to keep. The threshold can be configured via the property below (default: 10 recordings):

flightrecorder.old-recordings-max=10

A file will be removed when the status is STOPPED or CLOSED, based on a FIFO logic.

Trigger Flight Recording based on Micrometer Metrics

This starter allows automatic Flight Recording based on Micrometer Metrics. Using an application configuration file we can configure triggers based on SpEL (Spring Expression Language) which are evaluated on a regular basis. Once a trigger expression evaluates to true, a Flight Recording in started with a predefined duration and configuration. The most common setup would be to trigger a Flight Recording profiling once CPU usage is above a given value.

By default, this feature is enabled. In case you want to disable it, set the following property to false:

flightrecorder.trigger-enabled=false

This scheduled process is executed each 10 seconds. The default configuration can be changed thought this property:

flightrecorder.trigger-check-interval=10000

By default, this scheduled process is executed each 10 seconds. The default configuration can be changed thought this property:

flightrecorder.trigger-check-interval=10000

IMPORTANT: Be aware that the main app should be annotated with @EnableScheduling to enable the scheduled processes.

Here is a sample configuration file in YAML syntax:

flightrecorder:
  enabled: true  # is this starter active?
  recording-cleanup-interval: 5000 # try to cleanup old recordings every 5 seconds
  trigger-check-interval: 10000 # evaluate trigger expressions every 10 seconds
  trigger:
    - expression: meter('jvm.memory.used').tag('area','nonheap').tag('id','Metaspace').measurement('value') > 100
      startRecordingCommand:
        duration: 60
        timeUnit: SECONDS

The list of all created recordings can be seen as a JSON file using the following api:

http://localhost:8080/actuator/flightrecorder/

Advanced Configuration

Location of recordings

By default, all the recording files are stored at temporal system folder, ofter the "/tmp" folder. This base path can be changed through the following property:

flightrecorder:
  jfr-base-path: /my-path 

Custom configuration profile for recordings

By default, the used configuration is "<<JAVA_HOME>>/lib/jfr/profile.jfc". A custom configuration can be changed through the following property:

flightrecorder:
  jfr-custom-config: mycustomjfc 

NOTE: Just only the file's name (without extension) is required, not whole path.