Writing MultiNode tests

LAVA supports running a single test across multiple devices (of any type), combining those devices into a group. Devices within this MultiNode group can communicate with each other using the MultiNode API.

The test definitions used in MultiNode tests typically do not have to differ much from single-node tests, unless the tests need to support communication between devices in the same group. In fact, the recommended way to develop MultiNode tests is to start simple and build up complexity one step at a time. That’s what the examples here will show.

Note

When viewing MultiNode log files, the original YAML submitted to start the job is available via the MultiNode Definition link. Internally, LAVA parses and splits up that MultiNode definition into multiple sub-definitions, one per node in the test. Each node will then see a separate logical test job (and therefore a separate log file) based on these sub-definitions. They can be viewed via the Definition link. It is unlikely to be useful to submit the definition of one node of a MultiNode job as a separate job, due to links between the jobs.

Writing a MultiNode job file

Our first example is the simplest possible MultiNode test job - the same job runs on two devices of the same type, without using any of the synchronisation calls.

Defining MultiNode roles

Starting with an already-working simple single-device test job, the first changes to make are in device selection:

  • Remove the device_type declaration in the job; that only works for single devices.
  • Add configuration for the MultiNode protocol to tell LAVA how to select multiple devices for your test.

The MultiNode protocol defines the new concept of roles. This example snippet creates a group of two qemu devices, one in the foo role and one in the bar role.

protocols:
  lava-multinode:
    roles:
      foo:
        device_type: qemu
        context:
          arch: amd64
        count: 1
      bar:
        device_type: qemu
        context:
          arch: amd64
        count: 1
    timeout:
      minutes: 6

Note

The role is an arbitrary label - you may use whatever descriptive names you like for the different roles in your test, so long as they are unique.

Using the job context in MultiNode

The job context can be included in the MultiNode role and the same variables will be used for all devices within the specified role. See the example above for an example syntax.

The role names defined here will be used later in the test job to determine which tests are run on which devices, and also inside the test shell definition to determine how the devices communicate with each other. After just these changes, your test job will be enough to run a simple MultiNode test in LAVA. It will pick several devices for the test, then run exactly the same set of actions on each device independently.

Using MultiNode roles

The next thing to do is to modify the test job to use the roles that you have defined. This first example runs the same actions on both of the roles. Each action in the test definition should now include the role field and one or more label(s) to match those defined roles.

Here we deploy the same software to the foo and bar machines by specifying each role in a list:

actions:
- deploy:
    role:
    - foo
    - bar
    timeout:
      minutes: 5
    to: tmpfs
    images:
        rootfs:
          image_arg: -drive format=raw,file={rootfs}
          url: http://images.validation.linaro.org/kvm/standard/stretch-2.img.gz
          compression: gz
    os: debian
    root_partition: 1

We also use the same boot actions for all the devices:

- boot:
    timeout:
      minutes: 1
    role:
    - foo
    - bar
    method: qemu
    media: tmpfs
    auto_login:
      login_prompt: "debian login:"
      username: root
    prompts:
    - "root@debian:"

Running tests in MultiNode

By default, tests in MultiNode jobs will be run independently. If that is sufficient, the test action is very similar to that for a single-node job:

- test:
    role:
    - foo
    - bar
    timeout:
      minutes: 10
    definitions:
    - repository: http://git.linaro.org/lava-team/lava-functional-tests.git
      from: git
      path: lava-test-shell/multi-node/multinode01.yaml
      name: multinode-basic
    - repository: git://git.linaro.org/qa/test-definitions.git
      from: git
      path: ubuntu/smoke-tests-basic.yaml
      name: smoke-tests

That’s your first MultiNode test job complete. It’s quite simple to follow, but it hasn’t really done much yet. To see this in action, you could try the complete example test job yourself: first-multinode-job.yaml

Running different tests on different devices

As well as simply running the same tasks on similar devices, MultiNode can also run different tests on the different devices in the test. To configure this, use the role support to allocate different deploy, boot and test actions to different roles.

This second example will use two panda devices and one beaglebone-black device. These devices need different files to deploy and different commands to boot, and will most likely take different lengths of time to boot all the way to a login prompt. If you want to run this example test job yourself, you will need at least one beaglebone-black device and at least two panda devices.

The example includes details of how to deploy to devices using U-Boot, but don’t worry about those details. The important elements from a MultiNode perspective are the uses of role here.

Allocating different device types to a group

This is a simple change from our first example, defining the two roles of server and client:

protocols:
  lava-multinode:
    roles:
      server:
        device_type: cubietruck
        count: 1
      client:
        device_type: beaglebone-black
        count: 2
    timeout:
      minutes: 6

Splitting deployment actions between roles

Now we’re using different files in the deployment for each role. To support that, we define two separate deploy action blocks, one for the server machines and one for the client machines.

actions:
- deploy:
    role:
    - server
    timeout:
      minutes: 2
    to: tftp
    kernel:
      url: http://images.validation.linaro.org/snapshots.linaro.org/components/lava/standard/debian/jessie/armhf/4/vmlinuz
      type: zimage
    ramdisk:
      url: http://images.validation.linaro.org/snapshots.linaro.org/components/lava/standard/debian/jessie/armhf/4/initramfs.cpio.gz
      compression: gz
      add-header: u-boot
    modules:
      url: http://images.validation.linaro.org/snapshots.linaro.org/components/lava/standard/debian/jessie/armhf/4/modules.tar.gz
      compression: gz
    nfsrootfs:
      url: http://images.validation.linaro.org/snapshots.linaro.org/components/lava/standard/debian/jessie/armhf/4/jessie-armhf-nfs.tar.gz
      compression: gz
    os: debian
    dtb:
      url: http://images.validation.linaro.org/snapshots.linaro.org/components/lava/standard/debian/jessie/armhf/4/dtbs/sun7i-a20-cubietruck.dtb

- deploy:
    role:
    - client
    timeout:
      minutes: 2
    to: tftp
    kernel:
      url: http://images.validation.linaro.org/snapshots.linaro.org/components/lava/standard/debian/jessie/armhf/4/vmlinuz
      type: zimage
    ramdisk:
      url: http://images.validation.linaro.org/snapshots.linaro.org/components/lava/standard/debian/jessie/armhf/4/initramfs.cpio.gz
      compression: gz
      # the bootloader needs a u-boot header on the modified ramdisk
      add-header: u-boot
    modules:
      url: http://images.validation.linaro.org/snapshots.linaro.org/components/lava/standard/debian/jessie/armhf/4/modules.tar.gz
      compression: gz
    nfsrootfs:
      url: http://images.validation.linaro.org/snapshots.linaro.org/components/lava/standard/debian/jessie/armhf/4/jessie-armhf-nfs.tar.gz
      compression: gz
    os: debian
    dtb:
      url: http://images.validation.linaro.org/snapshots.linaro.org/components/lava/standard/debian/jessie/armhf/4/dtbs/am335x-boneblack.dtb

(Potentially) Splitting boot actions

To cover different boot commands we could now have two different boot action blocks. But in this case our devices behave in the same way in terms of bootup, so we can just use a single boot block and list both client and server.

- boot:
    role:
    - client
    - server
    method: u-boot
    commands: nfs
    auto_login:
      login_prompt: 'login:'
      username: root
    prompts:
    - 'root@jessie:'
    timeout:
      minutes: 5

Using MultiNode commands to synchronise devices

A very common requirement in a MultiNode test is that a device (or devices) within the MultiNode group must wait until another device in the group reaches a particular stage. This can be used to ensure that a device running a server has had time to complete the boot and start the server before the device running the client tries to make a connection to the server, for example. The only way to be sure that the server is ready for client connections is to make every client in the group wait until the server confirms that it is ready.

Continuing with the same panda and beaglebone-black example, let’s look at synchronising devices within a MultiNode group.

Controlling synchronisation from the test shell

Synchronisation is done using the MultiNode API, specifically the lava-send and lava-wait calls.

Continuing our example, we have two different versions of the test action block. In the version for the server role, the machine will do some work (in this case, install and start the Apache web server) and then tell the clients that the server is ready using lava-send:

- test:
    role:
    - server
    timeout:
      minutes: 5
    definitions:
    - repository:
        metadata:
          format: Lava-Test Test Definition 1.0
          name: apache-server
          description: "server installation"
          os:
          - debian
        run:
          steps:
          - apt -q update
          - apt -q -y install apache2
          - lava-test-case dpkg --shell dpkg -s apache2
          - lava-send server_installed
      from: inline
      name: apache-server
      path: inline/apache-server.yaml

Note

It is recommended to use inline definitions for the calls to the synchronisation helpers. This makes it much easier to debug when a synchronisation call times out and will allow the flow of the MultiNode job to be summarised in the UI.

The test definition specified for the client role causes the client devices to wait until the test definition specified for the server role uses lava-send to signal that the server is ready.

- test:
    role:
    - client
    timeout:
      minutes: 5
    definitions:
    - repository:
        metadata:
          format: Lava-Test Test Definition 1.0
          name: client-wait
          description: "client waiting for server"
          os:
          - debian
        run:
          steps:
          - lava-test-case client --shell uname -a
          - lava-wait server_installed
      from: inline
      name: client-wait
      path: inline/client-wait.yaml

This means that each device using the role client will wait until any one device in the group sends a signal with the messageID of server_installed. The assumption here is that the group only has one device with the label server.

The second MultiNode example is now complete. To run this yourself, you can see the complete example test job: second-multinode-job.yaml

HERE. Remember, you’ll need specific hardware devices for this to work.

Controlling synchronisation from the dispatcher

The MultiNode protocol also provides support for using the MultiNode API outside of the test shell definition; any action block can access the protocol from within specific actions. This makes it possible to even block deployment or boot on one group of machines until others are fully up and running, for example. There is a lot of flexibility here to allow for a massive range of possible test scenarios.

See also

Writing jobs using the MultiNode protocol for more information on how to call the MultiNode API outside the test shell.

Using the MultiNode API - further features

As demonstrated earlier, tests can use lava-wait to cause a device to wait on a single message from any other device in the MultiNode group. It is also possible to wait for all other devices in the MultiNode group send a signal - use lava-wait-all instead.

Each message sent using the MultiNode API uses a messageID, which is a string that must be unique within the group. It is recommended to make these strings descriptive to help track job progress and debug problems. Be careful to use underscores instead of spaces in the name. The messageID will be included in the log files of the test.

Warning

When using lava-wait and lava-wait-all, the device will wait until the expected messageID is received. If that messageID does not arrive, the job will simply wait forever and timeout when the default timeout expires. See Timeouts.

Using MultiNode commands to pass data between devices

lava-send can be used to send data between devices. A device can send data at any time, and that data will be broadcast to all devices in the MultiNode group. The data can be downloaded by any device in the group using the messageID using lava-wait or lava-wait-all. Data is sent as key-value pairs.

Note

The message data is stored in a cache file which will be overwritten when the next synchronisation call is made. Ensure that your scripts make use of (or copy aside) any MultiNode cache data before calling any other MultiNode API helpers that may clear the cache.

For example, if a device raises a network interface and wants to make data about that network connection available to other devices in the group, the device can send the IP address using lava-send:

run:
   steps:
      - lava-send ipv4 ip=$(./get_ip.sh)

The contents of get_ip.sh is operating system specific.

On the receiving device, the test definition would include a call to lava-wait or lava-wait-all with the same messageID:

run:
   steps:
      - lava-wait ipv4
      - ipdata=$(cat /tmp/lava_multi_node_cache.txt | cut -d = -f 2)

Note

Although multiple key value pairs can be sent as a single message, the API is not intended for large amounts of data. There is a message size limit of 4KiB, including protocol overhead. Use other transfer methods like ssh or wget if you need to send larger amounts of data between devices.

Helper tools in LAVA

LAVA provides some helper routines for common data transfer tasks and more can be added where appropriate. The main MultiNode API calls are intended to work on all POSIX systems, but some of the helper tools like lava-network may be restricted to particular operating systems or compatible shells due to a reliance on operating system tools like ifconfig.

Other MultiNode calls

It is also possible for devices to retrieve data about the group itself, including the role or name of the current device as well as the names and roles of other devices in the group. See MultiNode API for more information.

Writing jobs using the MultiNode protocol

The MultiNode protocol defines the MultiNode group and also allows actions within the job pipeline to make calls using the MultiNode API outside of a test definition.

The MultiNode protocol allows data to be shared between actions, including data generated in a test shell definition for one role being made available for use by a different role in its deploy or boot action.

The MultiNode protocol can underpin the use of other tools without necessarily needing a dedicated protocol class to be written for those tools. Using the MultiNode protocol is an extension of using the existing MultiNode API calls within a test definition. The use of the protocol is an advanced use of LAVA and relies on the test writer carefully planning how the job will work. See _delayed_start_multinode for an example of how to use this.