Set up Java profiling using Grafana Alloy

Grafana Alloy supports Java profiling. The collector configuration file is composed of components that are used to collect, transform, and send data. The Alloy configuration files use the Alloy configuration syntax.

Configure the components

The pyroscope.java component is used to continuously profile Java processes running on the local Linux OS using async-profiler.

pyroscope.java "java" {
  profiling_config {
    interval = "15s"
    alloc = "512k"
    cpu = true
    lock = "10ms"
    sample_rate = 100
  }
  forward_to = [pyroscope.write.endpoint.receiver]
  targets = discovery.relabel.java.output
}

Using the targets argument, you can specify which processes and containers to profile on the machine.

The targets can be from discovery.process component. You can use discovery.process join argument to join process targets with extra discoveries such as discovery.kubernetes, discovery.docker, and discovery.dockerswarm. You can use the discovery.relabel component to relabel discovered targets and set your own labels. For more information, refer to the Components documentation.

The forward_to parameter should point to a pyroscope.write component to send the collected profiles to your Pyroscope Server or Grafana Cloud.

Name	Type	Description	Default	Required
`targets`	`list(map(string))`	List of java process targets to profile.		yes
`forward_to`	`list(ProfilesReceiver)`	List of receivers to send collected profiles to.		yes
`tmp_dir`	`string`	Temporary directory to store async-profiler.	`/tmp`	no

The special label __process_pid__ must always be present in each target of targets and corresponds to the PID of the process to profile.

The special label service_name is required and must always be present. If service_name isn’t specified, pyroscope.java attempts to infer it from discovery meta labels. If service_name isn’t specified and couldn’t be inferred, then it’s set to unspecified.

The profiling_config block describes how async-profiler is invoked.

It supports the following arguments:

Name	Type	Description	Default	Required
`interval`	`duration`	How frequently to collect profiles from the targets.	“60s”	no
`cpu`	`bool`	A flag to enable CPU profiling, using `itimer` async-profiler event.	true	no
`sample_rate`	`int`	CPU profiling sample rate. It’s converted from Hz to interval and passed as `-i` arg to async-profiler.	100	no
`alloc`	`string`	Allocation profiling sampling configuration It’s passed as `--alloc` arg to async-profiler.	“512k”	no
`lock`	`string`	Lock profiling sampling configuration. It’s passed as `--lock` arg to async-profiler.	“10ms”	no

For more information on async-profiler configuration, see profiler-options.

Set privileges for the collector

You must run the collector, such Alloy, as root and inside host pid namespace for the pyroscope.java and discover.process components to work.

Start the collector

To start Grafana Alloy v1.2 and later, replace configuration.alloy with your configuration filename:

alloy run configuration.alloy

To start Grafana Alloy v1.0 or 1.1, replace configuration.alloy with your configuration file name:

alloy run --stability.level=public-preview configuration.alloy

The stability.level option is required for pyroscope.scrape with Alloy v1.0 or v1.1. For more information about stability.level, refer to the run command documentation.

Send data to Grafana Cloud Profiles

When sending to Grafana Cloud Profiles, you can use the following pyroscope.write component configuration which uses environment variables.

Ensure that you have appropriately configured the GC_URL, GC_USER, and GC_PASSWORD environment variables.

pyroscope.write "endpoint" {
    endpoint {
        basic_auth {
            password = env("GC_PASSWORD")
            username = env("GC_USER")
        }
        url = env("GC_URL")
    }
}

Examples

For more robust examples, refer to the Grafana Alloy and Agent Auto-instrumentation examples in the Pyroscope repository.

Profiling local process

discovery.process "all" {
}

discovery.relabel "java" {
    targets = discovery.process.all.targets
    // Filter only java processes
    rule {
        source_labels = ["__meta_process_exe"]
        action = "keep"
        regex = ".*/java$"
    }
    // Filter processes. For example: only processes with command line containing "FastSlow"
    rule {
        source_labels = ["__meta_process_commandline"]
        regex = "java FastSlow"
        action = "keep"
    }
    // Provide a service name for the process, otherwise it will be unspecified.
    rule {
        action = "replace"
        target_label = "service_name"
        replacement = "java-fast-slow"
    }
}

pyroscope.java "java" {
  forward_to = [pyroscope.write.example.receiver]
  targets = discovery.relabel.java.output
}

pyroscope.write "example" {
  endpoint {
    url = "http://pyroscope:4040"
  }
}

Profiling Docker containers

For a working example, refer to Java profiling via auto-instrumentation example in Docker.

discovery.docker "local_containers" {
  host = "unix:///var/run/docker.sock"
}

discovery.process "all" {
  join = discovery.docker.local_containers.targets
}

discovery.relabel "java" {
    targets = discovery.process.all.targets
    // Filter only java processes
    rule {
        source_labels = ["__meta_process_exe"]
        action = "keep"
        regex = ".*/java$"
    }
    // Filter only needed containers
    rule {
        source_labels = ["__meta_docker_container_name"]
        regex = ".*suspicious_pascal"
        action = "keep"
    }
    // Provide a service name for the process, otherwise it will default to the value of __meta_docker_container_name label.
    rule {
        action = "replace"
        target_label = "service_name"
        replacement = "java-fast-slow"
    }
}

pyroscope.java "java" {
  forward_to = [pyroscope.write.example.receiver]
  targets = discovery.relabel.java.output
}

pyroscope.write "example" {
  endpoint {
    url = "http://pyroscope:4040"
  }
}

Profiling Kubernetes pods

For a working example, refer to Grafana Alloy Java profiling via auto-instrumentation with Kubernetes.

discovery.kubernetes "local_pods" {
  selectors {
    field = "spec.nodeName=" + env("HOSTNAME")
    role = "pod"
  }
  role = "pod"
}

discovery.process "all" {
  join = discovery.kubernetes.local_pods.targets
}

discovery.relabel "java_pods" {
  targets = discovery.process.all.targets
  // Filter only java processes
  rule {
    source_labels = ["__meta_process_exe"]
    action = "keep"
    regex = ".*/java$"
  }
  rule {
    action = "drop"
    regex = "Succeeded|Failed|Completed"
    source_labels = ["__meta_kubernetes_pod_phase"]
  }
  rule {
    action = "replace"
    source_labels = ["__meta_kubernetes_namespace"]
    target_label = "namespace"
  }
  rule {
    action = "replace"
    source_labels = ["__meta_kubernetes_pod_name"]
    target_label = "pod"
  }
  rule {
    action = "replace"
    source_labels = ["__meta_kubernetes_pod_node_name"]
    target_label = "node"
  }
  rule {
    action = "replace"
    source_labels = ["__meta_kubernetes_pod_container_name"]
    target_label = "container"
  }
  // Provide arbitrary service_name label, otherwise it will be inferred from discovery labels automatically
  rule {
    action = "replace"
    regex = "(.*)@(.*)"
    replacement = "java/${1}/${2}"
    separator = "@"
    source_labels = ["__meta_kubernetes_namespace", "__meta_kubernetes_pod_container_name"]
    target_label = "service_name"
  }
  // Filter only needed services
  rule {
    action = "keep"
    regex = "(java/ns1/.*)|(java/ns2/container-.*0)"
    source_labels = ["service_name"]
  }
}

pyroscope.java "java" {
  forward_to = [pyroscope.write.example.receiver]
  targets = discovery.relabel.java.output
}

pyroscope.write "example" {
  endpoint {
    url = "http://pyroscope:4040"
  }
}