spotify / hype   0.0.18

Apache License 2.0 GitHub

Runs JVM closures in Docker containers on Kubernetes

Scala versions: 2.12 2.11




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Build Status Maven Central GitHub license

A library for seamlessly executing arbitrary JVM closures in Docker containers on Kubernetes.

User guide

Hype lets you execute arbitrary JVM code in a distributed environment where different parts might run concurrently in separate Docker containers, each using different amounts of memory, CPU and disk. With the help of Kubernetes and a cloud provider such as Google Cloud Platform, you'll have dynamically scheduled resources available for your code to utilize.

All this might sound a bit abstract, so let's run through a concrete example. We'll be using Scala for the examples, but all the core functionality is available from Java as well.



"com.spotify" %% "hype" % <version>

Run functions

In order to run functions on the cluster, you'll have to set up a Submitter value. The submitter encapsulates "where" to submit your functions.

val submitter = GkeSubmitter("gcp-project-id", "gce-zone-id", "gke-cluster-id", "gs://my-staging-bucket")

For testing, where you might want to run on a local Docker daemon, use LocalSubmitter(...).

Writing functions that can be executed with Hype is simple, just wrap them up as an HFn[T]. An HFn[T] is a closure that allows Hype to move the actual evaluation into a Docker container.

def example(arg: String) = HFn[String] {
  arg + " world!"

In the previous example, the default Hype Docker image (spotify/hype) is used. If you wish to use your own image, you can easily do so:

def example(arg: String) = HFn.withImage("") {
  arg + " world!"

Now we'll have to define the environment we want this function to run in.

val env = RunEnvironment()

Finally, use use the Submitter and RunEnvironment to execute an HFn[T]. When execution is complete, it'll return the function value back to your local context.

val result = submitter.submit(example("hello"), env.withRequest("cpu", "750m"))

Full example

This is a full example that runs a simple function that executes an arbitrary command and lists all environment variables. It uses the Scala sys.process package to execute commands in the function. Also see the docs on how to create k8s secrets

import sys.process._
import com.spotify.hype._

// A simple model for describing the runtime environment
case class EnvVar(name: String, value: String)
case class Res(cmdOutput: String, mounts: String, vars: List[EnvVar])

def extractEnv(cmd: String) = HFn[Res] {
  val cmdOutput = cmd !!
  val mounts = "df -h" !!
  val vars = for ((key, value) <- sys.env.toList)
    yield EnvVar(key, value)

  Res(cmdOutput, mounts, vars)

val submitter = GkeSubmitter("gcp-project-id", "gce-zone-id", "gke-cluster-id", "gs://my-staging-bucket")
val env = RunEnvironment()
    .withSecret("gcp-key", "/etc/gcloud") // a pre-created k8s secret volume named "gcp-key"

val res = submitter.submit(extractEnv("uname -a"), env)


The res.vars list returned should contain the environment variables that were present in the docker container while running on the cluster. Here's the output:

[info] Running HypeExample
[info] 22:15:14.211 | INFO | StagingUtil |> Uploading 69 files to staging location gs://my-staging-bucket to prepare for execution.
[info] 22:15:51.057 | INFO | StagingUtil |> Uploading complete: 4 files newly uploaded, 65 files cached
[info] 22:15:51.673 | INFO | Submitter  |> Submitting gs://my-staging-bucket/manifest-9vhb5u18.txt to RunEnvironment{base=RunEnvironment.SimpleBase{}, secretMounts=[Secret{name=gcp-key, mountPath=/etc/gcloud}], volumeMounts=[], resourceRequests={}}
[info] 22:15:52.221 | INFO | DockerRunner |> Created pod hype-run-mymlbuw8
[info] 22:15:52.351 | INFO | DockerRunner |> Pod hype-run-mymlbuw8 assigned to node gke-hype-test-default-pool-e1122946-fg9k
[info] 22:16:02.454 | INFO | DockerRunner |> Kubernetes pod hype-run-mymlbuw8 exited with status Succeeded
[info] 22:16:02.455 | INFO | DockerRunner |> Got termination message: gs://my-staging-bucket/continuation-993467547293976140-eUWBfwL9J2tHvWuJw0lU3g-hype-run-mymlbuw8-return.bin
[info] Linux hype-run-mymlbuw8 4.4.21+ #1 SMP Fri Feb 17 15:34:45 PST 2017 x86_64 GNU/Linux
[info] Filesystem      Size  Used Avail Use% Mounted on
[info] overlay          95G  4.1G   91G   5% /
[info] tmpfs           7.4G     0  7.4G   0% /dev
[info] tmpfs           7.4G     0  7.4G   0% /sys/fs/cgroup
[info] tmpfs           7.4G  4.0K  7.4G   1% /etc/gcloud
[info] /dev/sda1        95G  4.1G   91G   5% /etc/hosts
[info] tmpfs           7.4G   12K  7.4G   1% /run/secrets/
[info] shm              64M     0   64M   0% /dev/shm
[info] EnvVar(HYPE_EXECUTION_ID,hype-run-mymlbuw8)
[info] EnvVar(GOOGLE_APPLICATION_CREDENTIALS,/etc/gcloud/key.json)
[info] EnvVar(HOSTNAME,hype-run-cv7cln6y)
[info] EnvVar(PATH,/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin)
[info] EnvVar(JAVA_VERSION,8u121)
[info] EnvVar(KUBERNETES_SERVICE_HOST,xx.xx.xx.xx)

Leveraging implicits

In order to save some keystrokes, you can use our implicit operators:

import com.spotify.hype.magic._

Now you can set up an implicit Submitter value.

implicit val submitter = GkeSubmitter("gcp-project-id", "gce-zone-id", "gke-cluster-id", "gs://my-staging-bucket")

The environment value can also be declared implicit, but this is not required as it can explicitly be referenced when submitting functions.

implicit val env = RunEnvironment().withSecret("gcp-key", "/etc/gcloud")

Finally, use the #! (hashbang) operator to execute an HFn[T] in a given environment. It will use the Submitter and RunEnvironment which should be in scope.

val result = example("hello") #!

Using an implicit value as we did above works in most cases, but the hashbang (#!) operator also allows you to specify an explicit environment.

val result = example("hello") #! env.withRequest("cpu", "750m")

Custom environment images

In order for Hype to be able to execute functions in your custom Docker images, you'll have to install the hype-run command by adding the following to your Dockerfile:

# Install hype-run command
RUN /bin/sh -c "$(curl -fsSL"
ENTRYPOINT ["hype-run"]

It is important to have exactly this ENTRYPOINT as the Kubernetes Pods will expect to run the hype-run command.

See example Dockerfile

Process overview

This describes what Hype does from a high level point of view.

Persistent disk

Hype makes it easy to schedule persistent disk volumes across different closures in a workflow. A typical pattern seen in many use cases is to first use a disk in read-write mode to download and prepare some data, and then fork out to several parallel tasks that use the disk in read-only mode.

GCE Persistent Disk

In this example, we're using a StorageClass for GCE Persistent Disk that we've already set up on our cluster.

kind: StorageClass
  name: gce-ssd-pd
  type: pd-ssd

We can then request volumes from this StorageClass using the Hype API:

import sys.process._
import com.spotify.hype.magic._

implicit val submitter = GkeSubmitter("gcp-project-id",

// Create a 10Gi volume from the 'gce-ssd-pd' storage class
val ssd10Gi = TransientVolume("gce-ssd-pd", "10Gi")
val mount = "/usr/share/volume" 

val env = RunEnvironment()
val readWriteEnv = env.withMount(ssd10Gi.mountReadWrite(mount))
val readOnlyEnv = env.withMount(ssd10Gi.mountReadOnly(mount))

def write = HFn[Int] {
  // get a random word and store it in the volume
  s"curl -so $mount/word" !

def read = HFn[String] {
  // read the word file
  s"cat $mount/word" !!

// Write to the volume
write #! readWriteEnv

// Run 10 parallel functions that have read only access to the volume
val results = for (_ <- Range(0, 10).par)
    yield read #! readOnlyEnv

The submissions from the parallel range will each run concurrently in separate pods and have read-only access to the /usr/share/volume mount. The volume should contain the random word that was written to it from the write function.

Coordinating metadata and parameters across multiple submissions should be just as trivial as passing values from function calls as arguments to other functions.

Volume re-use

By default, the backing claim for a TransientVolume on Kubernetes is deleted when the JVM terminates.

If you wish to persist the Volume between invocations, you can use:

val disk = PersistentVolume("my-persistent-volume", "gce-ssd-pd", "10Gi")

If the volume does not exist, it will be created. Subsequent invocations will return use already created volume.

This is useful in use cases with larger volumes that take a significant amount of time to load, or when there's some sort of workflow orchestration around the Hype code that might run different parts in separate JVM invocations.

Environment Pod from YAML

Sometimes more control over the Kubernetes Pod is desired. For these cases a regular Pod YAML file can be used as a base for the RunEnvironment. Hype will still manage any used Volume Claims and mounts, but will leave all other details as you've specified them.

Hype will expect at least this field to be specified:

  • spec.containers[name:hype-run] - There must at least be a container named hype-run

Please note that the image field should not bet set (Hype requires each module to define its image).

Hype will override the spec.containers[name:hype-run].args field, so don't set it.

Here's a minimal Pod YAML file with some custom settings, ./src/main/resources/pod.yaml:

apiVersion: v1
kind: Pod

  restartPolicy: Never # do not retry on failure

  - name: hype-run
    imagePullPolicy: Always # pull the image on each run

    env: # additional environment variables
    - name: EXAMPLE
      value: my-env-value

Any resource requests added through the RunEnvironment API will merge with, and override the ones set in the YAML file.

Then simply load your RunEnvironment through

val env = RunEnvironmentFromYaml("/pod.yaml")

This project is in early development stages, expect anything you see to change.