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Testing Autoscaling Locally

Testing autoscaling behavior is important for autoscaler development and the debugging of applications that depend on autoscaler behavior. You can run the autoscaler locally without needing to launch a real cluster with one of the following methods:

Using RAY_FAKE_CLUSTER=1 ray start

Instructions:

  1. Navigate to the root directory of the Ray repo you have cloned locally.
  2. Locate the fake_multi_node/example.yaml example file and fill in the number of CPUs and GPUs the local machine has for the head node type config. The YAML follows the same format as cluster autoscaler configurations, but some fields are not supported.
  3. Configure worker types and other autoscaling configs as desired in the YAML file.
  4. Start the fake cluster locally:
$ ray stop --force
$ RAY_FAKE_CLUSTER=1 ray start \
    --autoscaling-config=./python/ray/autoscaler/_private/fake_multi_node/example.yaml \
    --head --block
  1. Connect your application to the fake local cluster with ray.init("auto").
  2. Run ray status to view the status of your cluster, or cat /tmp/ray/session_latest/logs/monitor.* to view the autoscaler monitor log:
$ ray status
======== Autoscaler status: 2021-10-12 13:10:21.035674 ========
Node status
---------------------------------------------------------------
Healthy:
 1 ray.head.default
 2 ray.worker.cpu
Pending:
 (no pending nodes)
Recent failures:
 (no failures)

Resources
---------------------------------------------------------------
Usage:
 0.0/10.0 CPU
 0.00/70.437 GiB memory
 0.00/10.306 GiB object_store_memory

Demands:
 (no resource demands)

Using ray.cluster_utils.AutoscalingCluster

To programmatically create a fake multi-node autoscaling cluster and connect to it, you can use cluster_utils.AutoscalingCluster. Here's an example of a basic autoscaling test that launches tasks triggering autoscaling:

/../../python/ray/tests/test_autoscaler_fake_multinode.py

Python documentation:

ray.cluster_utils.AutoscalingCluster

Features and Limitations of fake_multinode

Most of the features of the autoscaler are supported in fake multi-node mode. For example, if you update the contents of the YAML file, the autoscaler will pick up the new configuration and apply changes, as it does in a real cluster. Node selection, launch, and termination are governed by the same bin-packing and idle timeout algorithms as in a real cluster.

However, there are a few limitations:

  1. All node raylets run uncontainerized on the local machine, and hence they share the same IP address. See the fake_multinode_docker <fake-multinode-docker> section for an alternative local multi node setup.
  2. Configurations for auth, setup, initialization, Ray start, file sync, and anything cloud-specific are not supported.
  3. It's necessary to limit the number of nodes / node CPU / object store memory to avoid overloading your local machine.

Testing containerized multi nodes locally with Docker compose

To go one step further and locally test a multi node setup where each node uses its own container (and thus has a separate filesystem, IP address, and Ray processes), you can use the fake_multinode_docker node provider.

The setup is very similar to the fake_multinode <fake-multinode> provider. However, you need to start a monitoring process (docker_monitor.py) that takes care of running the docker compose command.

Prerequisites:

  1. Make sure you have docker installed.
  2. Make sure you have the docker compose V2 plugin installed.

Using RAY_FAKE_CLUSTER=1 ray up

Instructions:

  1. Navigate to the root directory of the Ray repo you have cloned locally.
  2. Locate the fake_multi_node/example_docker.yaml example file and fill in the number of CPUs and GPUs the local machine has for the head node type config. The YAML follows the same format as cluster autoscaler configurations, but some fields are not supported.
  3. Configure worker types and other autoscaling configs as desired in the YAML file.
  4. Make sure the shared_volume_dir is empty on the host system
  5. Start the monitoring process:
$ python ./python/ray/autoscaler/_private/fake_multi_node/docker_monitor.py \
    ./python/ray/autoscaler/_private/fake_multi_node/example_docker.yaml
  1. Start the Ray cluster using ray up:
$ RAY_FAKE_CLUSTER=1 ray up -y ./python/ray/autoscaler/_private/fake_multi_node/example_docker.yaml
  1. Connect your application to the fake local cluster with ray.init("ray://localhost:10002").
  2. Alternatively, get a shell on the head node:
$ docker exec -it fake_docker_fffffffffffffffffffffffffffffffffffffffffffffffffff00000_1 bash

Using ray.autoscaler._private.fake_multi_node.test_utils.DockerCluster

This utility is used to write tests that use multi node behavior. The DockerCluster class can be used to setup a Docker-compose cluster in a temporary directory, start the monitoring process, wait for the cluster to come up, connect to it, and update the configuration.

Please see the API documentation and example test cases on how to use this utility.

ray.autoscaler._private.fake_multi_node.test_utils.DockerCluster

Features and Limitations of fake_multinode_docker

The fake multinode docker node provider provides fully fledged nodes in their own containers. However, some limitations still remain:

  1. Configurations for auth, setup, initialization, Ray start, file sync, and anything cloud-specific are not supported (but might be in the future).
  2. It's necessary to limit the number of nodes / node CPU / object store memory to avoid overloading your local machine.
  3. In docker-in-docker setups, a careful setup has to be followed to make the fake multinode docker provider work (see below).

Shared directories within the docker environment

The containers will mount two locations to host storage:

  • /cluster/node: This location (in the container) will point to cluster_dir/nodes/<node_id> (on the host). This location is individual per node, but it can be used so that the host can examine contents stored in this directory.
  • /cluster/shared: This location (in the container) will point to cluster_dir/shared (on the host). This location is shared across nodes and effectively acts as a shared filesystem (comparable to NFS).

Setting up in a Docker-in-Docker (dind) environment

When setting up in a Docker-in-Docker (dind) environment (e.g. the Ray OSS Buildkite environment), some things have to be kept in mind. To make this clear, consider these concepts:

  • The host is the not-containerized machine on which the code is executed (e.g. Buildkite runner)
  • The outer container is the container running directly on the host. In the Ray OSS Buildkite environment, two containers are started - a dind network host and a container with the Ray source code and wheel in it.
  • The inner container is a container started by the fake multinode docker node provider.

The control plane for the multinode docker node provider lives in the outer container. However, docker compose commands are executed from the connected docker-in-docker network. In the Ray OSS Buildkite environment, this is the dind-daemon container running on the host docker. If you e.g. mounted /var/run/docker.sock from the host instead, it would be the host docker daemon. We will refer to both as the host daemon from now on.

The outer container modifies files that have to be mounted in the inner containers (and modified from there as well). This means that the host daemon also has to have access to these files.

Similarly, the inner containers expose ports - but because the containers are actually started by the host daemon, the ports are also only accessible on the host (or the dind container).

For the Ray OSS Buildkite environment, we thus set some environment variables:

  • RAY_TEMPDIR="/ray-mount". This environment variable defines where the temporary directory for the cluster files should be created. This directory has to be accessible by the host, the outer container, and the inner container. In the inner container, we can control the directory name.
  • RAY_HOSTDIR="/ray". In the case where the shared directory has a different name on the host, we can rewrite the mount points dynamically. In this example, the outer container is started with -v /ray:/ray-mount or similar, so the directory on the host is /ray and in the outer container /ray-mount (see RAY_TEMPDIR).
  • RAY_TESTHOST="dind-daemon" As the containers are started by the host daemon, we can't just connect to localhost, as the ports are not exposed to the outer container. Thus, we can set the Ray host with this environment variable.

Lastly, docker-compose obviously requires a docker image. The default docker image is rayproject/ray:nightly. The docker image requires openssh-server to be installed and enabled. In Buildkite we build a new image from rayproject/ray:nightly-py37-cpu to avoid installing this on the fly for every node (which is the default way). This base image is built in one of the previous build steps.

Thus, we set

  • RAY_DOCKER_IMAGE="rayproject/ray:multinode-py37"
  • RAY_HAS_SSH=1

to use this docker image and inform our multinode infrastructure that SSH is already installed.

Local development

If you're doing local development on the fake multi node docker module, you can set

  • FAKE_CLUSTER_DEV="auto"

this will mount the ray/python/ray/autoscaler directory to the started nodes. Please note that this is will probably not work in your docker-in-docker setup.

If you want to to specify which top-level Ray directories to mount, you can use e.g.

  • FAKE_CLUSTER_DEV_MODULES="autoscaler,tune"

This will mount both ray/python/ray/autoscaler and ray/python/ray/tune within the node containers. The list of modules should be comma separated and without spaces.