Simple Administration

Outline

LAVA is complex and administering a LAVA instance can be an open-ended task covering a wide range of skills.

  • Debian system administration
  • Device integration
  • Network configuration
  • Writing tests
  • Triage
  • Python/Django knowledge - for debugging

Debian system administration

At a simple level, LAVA requires a variety of Debian system administration tasks, including:

  • installing, upgrading and maintaining the installed packages and apt sources

  • configuring services outside LAVA, including:

    • apache - LAVA provides an example apache configuration but many instances will need to adapt this for their own hosting requirements.

    • DHCP - Most devices will need networking support using DHCP.

    • configuration management - LAVA has a variety of configuration files and a number of other services and tools will also need to be configured, for example serial console services, TFTP services and authentication services.

      See also

      Creating Backups

    • email - LAVA can use email for notifications, if test writers include appropriate requests in the test job submissions. To send email, LAVA relies on the basic Django email support using a standard sendmail interface. Only the master needs to be configured to send email, notifications from workers are handled via the master.

Infrastructure

LAVA instances will need some level of infrastructure, including:

  • UPS
  • network switches
  • remote power control hardware
  • master and worker hardware

Many instances will also require specialised hardware to assist with the automation of specific devices, including switchable USB hubs or specialised relay boards.

Start small

These rules may seem harsh or obvious or tedious. However, multiple people have skipped one or more of these requirements and have learnt that these steps provide valuable advice and assistance that can dramatically improve your experience of LAVA. Everyone setting up LAVA, is strongly advised to follow all of these rules.

  1. Start with a minimal LAVA install with at most one or two devices - at this stage only QEMU devices should be considered. This provides the best platform for learning LAVA, before learning how to administer a LAVA instance.

  2. Use the worked examples in the documentation which refer back to standard builds and proven test jobs. There will be enough to do in becoming familiar with how to fix problems and issues local to your own instance without adding the complexity of devices or kernel builds to which only you have access.

  3. Avoid rushing to your custom device - device integration into any automated system is hard. It does not become any easier if you are trying to learn how to use the automation as well.

  4. Plan how to test

    • use the examples and device types which are known to work.
    • Read through all the worked examples before starting your planning, there are likely to be useful ways to do what you want to do and advice on why it is a bad idea to do some of the things you may have considered at the start.
    • plan out how to do the testing of other custom devices by looking for similar device support already available in other LAVA instances.
    • Avoid shortcuts - it may seem that you only want to connect & test but there are known problems with overly simplistic approaches and you are likely to need to use deploy actions and boot actions to be able to produce reliable results.
  5. Have at least one test instance. A single instance of LAVA is never sufficient for any important testing. Everyone needs at least one test instance in a VM or on another machine to have confidence that administrative changes will not interfere with test jobs.

  6. Control your changes - configuration, test job definitions, test shell definitions, device dictionaries, template changes and any code changes - all need to be in version control.

  7. Control access to the dispatcher and devices - device configuration details like the connection command and remote power commands can be viewed by all users who are able to submit to that device. In many cases, these details are sufficient to allow anyone with the necessary access to administer those devices, including modifying bootloader configuration. Only administrators should have access to any machine which itself has access to the serial console server and/or remote power control services. Typically, this will be controlled using SSH keys.

    See also

    Power Commands

  8. Subscribe to the Mailing lists where you will find others who have setup their own LAVA instances. IRC is fine for quick queries but it is trivial to lose track of previous comments, examples and links when the channel gets busy. Mailing lists have public archives which are fully indexed by search engines. The archives will help you solve your current issue and help many others find answers for their own issues later.

Problems with simplistic testing

There are a number of common fallacies relating to automation. Check your test ideas against these before starting to make your plans:

Connect and test

Seems simple enough - it doesn’t seem as if you need to deploy a new kernel or rootfs every time, no need to power off or reboot between tests. Just connect and run stuff. After all, you already have a way to manually deploy stuff to the board.

  • The biggest problem with this method is Persistence - LAVA keeps the LAVA components separated from each other but tests frequently need to install support which will persist after the test, write files which can interfere with other tests or break the manual deployment in unexpected ways when things go wrong.
  • The second problem within this fallacy is simply the power drain of leaving the devices constantly powered on. In manual testing, you would apply power at the start of your day and power off at the end. In automated testing, these devices would be on all day, every day, because test jobs could be submitted at any time.

ssh instead of serial

This is an over-simplification which will lead to new and unusual bugs and is only a short step on from connect & test with many of the same problems. A core strength of LAVA is demonstrating differences between types of devices by controlling the boot process. By the time the system has booted to the point where sshd is running, many of those differences have been swallowed up in the boot process.

ssh can be useful within LAVA tests but using ssh to the exclusion of serial means that the boot process is hidden from the logs, including any errors and warnings. If the boot process results in a system which cannot start sshd or cannot expose ssh over the network, the admin has no way to determine the cause of the failure. If the userspace tests fail, the test writer cannot be sure that the boot process was not a partial cause of the failure as the boot process messages are not visible. This leads to test writers repeatedly submitting the same jobs and wasting a lot of time in triage because critical information is hidden by the choice of using ssh instead of serial.

Using ssh without a boot process at all has all the same problems as Connect and test.

Limiting all your tests to userspace without changing the running kernel is not making the best use of LAVA. LAVA has a steep learning curve, but trying to cut corners won’t help you in the long run. If you see ssh as a shortcut, it is probable that your use case may be better served by a different tool which does not control the boot process, for example tools based on containers and virtual machines.

Note

Using serial also requires some level of automated power control. The connection is made first, then power is applied and there is no allowance for manual intervention in applying power. LAVA is designed as a fully automated system where test jobs can run reliably without any manual operations.

test everything at the same time

You’ve built an entire system and now you put the entire thing onto the device and do all the tests at the same time. There are numerous problems with this approach:

  1. Breaking the basic scientific method of test one thing at a time. The single system contains multiple components, like the kernel and the rootfs and the bootloader. Each one of those components can fail in ways which can only be picked up when some later component produces a completely misleading and unexpected error message.
  2. Timing - simply deploying the entire system for every single test job wastes inordinate amounts of time when you do finally identify that the problem is a configuration setting in the bootloader or a missing module for the kernel.
  3. Reproducibility - the larger the deployment, the more complex the boot and the tests become. Many LAVA devices are prototypes and development boards, not production servers. These devices will fail in unpredictable places from time to time. Testing a kernel build multiple times is much more likely to give you consistent averages for duration, performance and other measurements than if the kernel is only tested as part of a complete system.
  4. Automated recovery - deploying an entire system can go wrong, whether an interrupted copy or a broken build, the consequences can mean that the device simply does not boot any longer.
    • Every component involved in your test must allow for automated recovery. This means that the boot process must support being interrupted before that component starts to load. With a suitably configured bootloader, it is straightforward to test kernel builds with fully automated recovery on most devices. Deploying a new build of the bootloader itself is much more problematic. Few devices have the necessary management interfaces with support for secondary console access or additional network interfaces which respond very early in boot. It is possible to chainload some bootloaders, allowing the known working bootloader to be preserved.

I already have builds

This may be true, however, automation puts extra demands on what those builds are capable of supporting. When testing manually, there are any number of times when a human will decide that something needs to be entered, tweaked, modified, removed or ignored which the automated system needs to be able to understand. Examples include:

  • /etc/resolv.conf - it is common for many build tools to generate or copy a working /etc/resolv.conf based on the system within which the build tool is executed. This is a frequent cause of test jobs failing due to being unable to lookup web addresses using DNS. It is also common for an automated system to be in a different network subnet to the build tool, again causing the test job to be unable to use DNS due to the wrong data in /etc/resolv.conf.
  • Customised tools - using non-standard build tools or putting custom scripts, binaries and programs into a root filesystem is a common reason for test jobs to fail when users migrate to updated builds.
  • Comparability - LAVA has various ways to support local admins but to make sense of logs or bug reports, the test job needs to be comparable to one already known to work elsewhere.

Make use of the standard files for known working device types. These files come with details of how to rebuild the files, logs of the each build and checksums to be sure the download is correct.

Automation can do everything

It is not possible to automate every test method. Some kinds of tests and some kinds of devices lack critical elements that do not work well with automation. These are not problems in LAVA, these are design limitations of the kind of test and the device itself. Your preferred test plan may be infeasible to automate and some level of compromise will be required.

Users are all admins too

This will come back to bite! However, there are other ways in which this can occur even after administrators have restricted users to limited access. Test jobs (including hacking sessions) have full access to the device as root. Users, therefore, can modify the device during a test job and it depends on the device hardware support and device configuration as to what may happen next. Some devices store bootloader configuration in files which are accessible from userspace after boot. Some devices lack a management interface that can intervene when a device fails to boot. Put these two together and admins can face a situation where a test job has corrupted, overridden or modified the bootloader configuration such that the device no longer boots without intervention. Some operating systems require a debug setting to be enabled before the device will be visible to the automation (e.g. the Android Debug Bridge). It is trivial for a user to mistakenly deploy a default or production system which does not have this modification.

Administrators need to be mindful of the situations from which users can (mistakenly or otherwise) modify the device configuration such that the device is unable to boot without intervention when the next job starts. This is one of the key reasons for health checks to run sufficiently often that the impact on other users is minimised.

Roles of LAVA administrators

The ongoing roles of administrators include:

  • monitor the number of devices which are online

  • identify the reasons for health check failures

  • communicate with users when a test job has made the device unbootable (i.e. bricked)

  • recover devices which have gone offline

  • restrict command line access to the dispatcher(s) and device(s) to only other administrators. This includes access to the serial console server and the remote power control service. Ideally, users must not have any access to the same subnet as the dispatchers and devices, except for the purposes of accessing devices during LAVA Hacking Sessions. This may involve port forwarding or firewall configuration and is not part of the LAVA software support.

  • to keep the instance at a sufficiently high level of reliability that Continuous Integration produces results which are themselves reliable and useful to the developers. To deliver this reliability, administrators do need to sometimes prevent users from making mistakes which are likely to take devices offline.

  • prepare and routinely test backups and disaster recovery support. Many lab admin teams use salt or ansible or other configuration management software. Always ensure you have a fast way of deploying a replacement worker or master in case of hardware failure.

    See also

    Creating Backups for details of what to backup and test.

Best practice

See also

Creating Backups

  • Before you upgrade the server or dispatcher, run the standard test jobs and a few carefully chosen stable jobs of your own as a set of functional tests - just as the LAVA team do upstream.
  • Keep all the servers and dispatchers regularly updated with regard to security updates and bug fixes. The more often you run the upgrades, the fewer packages will be involved in each upgrade and so the easier it will be to spot that one particular upgrade may be misbehaving.
  • Repeat your functional tests after all upgrades.
  • Use health checks and tweak the frequency so that busy devices run health checks often enough to catch problems early.
  • Add standard investigative tools. You may choose to use nagios and / or munin or other similar tools.
  • Use configuration management. Various LAVA instances use salt or puppet or ansible. Test out various tools and make your own choice.

Triage

When you come across problems with your LAVA instance, there are some basic information sources, methods and tools which will help you identify the problem(s).

Problems affecting test jobs

Administrators may be asked to help with debugging test jobs or may need to use test jobs to investigate some administration problems, especially health checks.

  • Start with the triage guidelines if the problem shows up in test jobs.
  • Check the Job failure comment for information on exactly what happened.
  • Specific LAVA Failure messages may relate directly to an admin issue.
  • Try to reproduce the failure with smaller and less complex test jobs, where possible.

Some failure comments in test jobs are directly related to administrative problems.

Power up failures

  • If the device dictionary contains errors, it is possible that the test job is trying to turn on power to or read serial input from the wrong ports. This will show up as a timeout when trying to connect to the device.

    Note

    Either the PDU command or the connection command could be wrong. If the device previously operated normally, check the details of the power on and connection commands in previous jobs. Also, try running the power on command followed by the connection command manually (as root) on the relevant worker.

    • If the ports are correct, check that the specified PDU port is actually delivering power when the state of the port is reported as ON and switching off power when reporting OFF. It is possible for individual relays in a PDU to fail, reporting a certain state but failing to switch the relay when the state is reported as changing. Once a PDU starts to fail in this way, the PDU should be replaced as other ports may soon fail in the same manner. (Checking the light or LED on the PDU port may be insufficient. Try connecting a fail safe device to the port, like a desk light etc. This may indicate whether the board itself has a hardware problem.)
    • If the command itself is wrong or returns non-zero, the test job will report an Infrastructure Error
  • If the connection is refused, it is possible that the device node does not (yet) exist on the worker. e.g. check the ser2net configuration and the specified device node for the port being used.

  • Check whether the device needs specialised support to avoid issues with power reset buttons or other hardware modes where the device does not start to boot as soon as power is applied. Check that any such support is actually working.

Compatibility failures

Dispatcher unable to meet job compatibility requirement.

The master uses the lava-dispatcher code on the server to calculate a compatibility number - the highest integer in the strategy classes used for that job. The worker also calculates the number and unless these match, the job is failed.

The compatilibilty check allows the master to detect if the worker is running older software, allowing the job to fail early. Compatibility is changed when existing support is removed, rather than when new code is added. Admins remain responsible for ensuring that if a new device needs new functionality, the worker will need to be running updated code.

See also

Missing methods and Python traceback messages. Also the developer documentation for more information on how developers set the compatibility for test jobs.

Checking for MultiNode issues

  • Check the contents of /etc/lava-coordinator/lava-coordinator.conf on the worker. If you have multiple workers, all workers must have coordinator configuration pointing at a single lava-coordinator which serves all workers on that instance (you can also have one coordinator for multiple instances).

  • Check the output of the lava-coordinator logs in /var/log/lava-coordinator.log.

  • Run the status check script provided by lava-coordinator:

    $ /usr/share/lava-coordinator/status.py
    status check complete. No errors
    
  • Use the example test jobs to distinguish between adminstration errors and test job errors. Simplify and make your test conditions portable. MultiNode is necessarily complex and can be hard to debug.

    • Use QEMU to allow the test job to be submitted to other instances.
    • Use anonymous git repositories for test definitions that just show the problem, without needing to access internal resources
    • Use inline test definitions so that the steps can be seen directly in the test job submission. This makes it easier to tweak and test as well as making it easier for others to help in the work.

Where to find debug information

index:: jinja2 template administration

Jinja2 Templates

LAVA uses Jinja2 to allow devices to be configured using common data blocks, inheritance and the device-specific device dictionary. Templates are developed as part of lava-server with supporting unit tests:

lava-server/lava_scheduler_app/tests/device-types/

Building a new package using the developer scripts will cause the updated templates to be installed into:

/etc/lava-server/dispatcher-config/device-types/

The jinja2 templates support conditional logic, iteration and default arguments and are considered as part of the codebase of lava-server. Changing the templates can adversely affect other test jobs on the instance. All changes should be made first as a developer. New templates should be accompanied by new unit tests for that template.

Note

Although these are configuration files and package updates will respect any changes you make, please talk to us about changes to existing templates maintained within the lava-server package.

Log files

  • lava-master - controls all V2 test jobs after devices have been assigned. Logs are created on the master:

    /var/log/lava-server/lava-master.log
    
  • lava-logs - aggregate the test job logs produced by the dispatchers. Logs are created on the master:

    /var/log/lava-server/lava-logs.log
    
  • lava-scheduler - controls how all devices are assigned. Control will be handed over to lava-master once V1 code is removed. Logs are created on the master:

    /var/log/lava-server/lava-scheduler.log
    
  • lava-slave - controls the operation of the test job on the slave. Includes details of the test results recorded and job exit codes. Logs are created on the slave:

    /var/log/lava-dispatcher/lava-slave.log
    
  • apache - includes XML-RPC logs:

    /var/log/apache2/lava-server.log
    
  • gunicorn - details of the WSGI operation for django:

    /var/log/lava-server/gunicorn.log
    

TestJob data

  • slave logs are transmitted to the master - temporary files used by the testjob are deleted when the test job ends.

  • job validation - the master retains the output from the validation of the testjob performed by the slave. The logs is stored on the master as the lavaserver user - so for job ID 4321:

    $ sudo su lavaserver
    $ ls /var/lib/lava-server/default/media/job-output/job-4321/description.yaml
    
  • other testjob data - also stored in the same location on the master are the complete log file (output.yaml) and the logs for each specific action within the job in a directory tree below the pipeline directory.

LAVA configuration files

See also

Creating Backups

lava-coordinator

  • lava-coordinator.conf - /etc/lava-coordinator/lava-coordinator.conf contains the lookup information for workers to find the lava-coordinator for multinode test jobs. Each worker must share a single lava-coordinator with all other workers attached to the same instance. Instances may share a lava-coordinator with other instances or can choose to have one each, depending on expected load and maintenance priorities. The lava-coordinator daemon itself does not need to be installed on a master but that is the typical way to use the coordinator.

    Caution

    Restarting lava-coordinator will cause errors for any running MultiNode test job. However, changes to /etc/lava-coordinator/lava-coordinator.conf on a worker can be made without needing to restart the lava-coordinator daemon itself.

lava-dispatcher

Files and directories in /etc/lava-dispatcher/:

  • lava-slave - Each slave needs configuration to be able to locate the correct master using ZMQ. This involves a URL for a ZMQ socket on the master and optionally the location of the ZMQ certificates to support authentication and encryption of the ZMQ messages.

  • certificates.d/ - On a worker, this directory contains the master certificate for each worker. On a master, this directory contains a copy of the certificate for each worker which is allowed to connect to the master.

lava-server

Files and directories in /etc/lava-server/:

  • dispatcher.d - worker specific configuration. Files in this directory need to be created by the admin and have a filename which matches the reported hostname of the worker in /var/log/lava-server/lava-master.log.

  • dispatcher-config - contains V2 device configuration, including Device type templates and V2 health checks.

  • env.yaml - Configures the environment that will be used by the server and the dispatcher. This can be used to modify environment variables to support a proxy or other lab-specific requirements. The file is part of the lava-server package and contains comments on how changes can be made.

  • instance.conf - Local database configuration for the master. This file is managed by the package installation process.

  • lava-master - Each master needs configuration to set up the correct ZMQ ports on the master. This involves a URL for a ZMQ socket on the master and optionally the location of the ZMQ certificates to support authentication and encryption of the ZMQ messages.

  • lava-server-gunicorn.service - example file for a systemd service to run lava-server-gunicorn instead of letting systemd generate a service file from the sysvinit support included in the package.

  • secret_key.conf - This key is used by Django to ensure the security of various cookies and # one-time values. To learn more please visit: http://docs.djangoproject.com/en/1.8/ref/settings/#secret-key.

  • settings.conf - Instance-specific settings used by Django and lava-server including authentication backends, branding support and event notifications.

Overriding device configuration

Some device configuration can be overridden without making changes to the Jinja2 Templates. This does require some understanding of how template engines like jinja2 operate.

  • Values hard-coded into the jinja2 template cannot be overridden. The template would need to be modified and re-tested.
  • Variables in the jinja2 template typically have a default value.
  • Variables in the jinja2 template can be override the default in the following sequence:
    1. by the next template
    2. by the device dictionary or, if neither of those set the variable
    3. by the job context.

To identify which variables can be overridden, check the template for placeholders. A commonly set value for QEMU device types is the amount of memory (on the dispatcher) which QEMU will be allowed to use for each test job:

- -m {{ memory|default(512) }}

Most administrators will need to set the memory constraint in the device dictionary so that test jobs cannot allocate all the available memory and cause the dispatcher to struggle to provide services to other test jobs. An example device dictionary to override the default (and also prevent test jobs from setting a different value) would be:

{% extends 'qemu.jinja2' %}
{% set memory = 1024 %}

Admins need to balance the memory constraint against the number of other devices on the same dispatcher. There are occassions when multiple test jobs can start at the same time, so admins may also want to limit the number of emulated devices on any one dispatcher to the number of cores on that dispatcher and set the amount of memory so that with all devices in use there remains some memory available for the system itself.

Most administrators will not set the arch variable of a QEMU device so that test writers can use the one device to run test jobs using a variety of architectures by setting the architecture in the job context. The QEMU template has conditional logic for this support:

{% if arch == 'arm64' or arch == 'aarch64' %}
           qemu-system-aarch64
{% elif arch == 'arm' %}
           qemu-system-arm
{% elif arch == 'amd64' %}
           qemu-system-x86_64
{% elif arch == 'i386' %}
           qemu-system-x86
{% endif %}

Note

Limiting QEMU to specific architectures on dispatchers which are not able to safely emulate an x86_64 machine due to limited memory or number of cores is an advanced admin task. Device tags will be needed to ensure that test jobs are properly scheduled.

Overriding device constants

The dispatcher uses a variety of constants and some of these can be overridden in the device configuration.

A common override used when operating devices on your desk or when a PDU is not available, allows the dispatcher to recognise a soft reboot. Another example is setting up the kernel starting message that the LAVA will recognize during boot time. This uses the shutdown_message and boot_message keys in the constants section of the device config:

{% extends 'my-device.jinja2' %}
{% set shutdown_message = "reboot: Restarting system" %}
{% set boot_message = "Booting Linux" %}

Some of the constants can also be overridden in the test job definition, i.e. looking at the same example shutdown-message parameter support in the u-boot boot action:

- boot:
   method: u-boot
   commands: ramdisk
   parameters:
     shutdown-message: "reboot: Restarting system"
   prompts:
   - 'linaro-test'
   timeout:
     minutes: 2

Adding more devices

Note

If you are considering using MultiNode in your Test Plan, now is the time to ensure that MultiNode jobs can run successfully on your instance.

Once you have a couple of QEMU devices running and you are happy with how to maintain, debug and test using those devices, start adding known working devices. These are devices which already have templates in:

/etc/lava-server/dispatcher-config/device-types/

The majority of the known device types are low-cost ARM developer boards which are readily available. Even if you are not going to use these boards for your main testing, you are recommended to obtain a couple of these devices as these will make it substantially easier to learn how to administer LAVA for any devices other than emulators.

Physical hardware like these dev-boards have hardware requirements like:

  • serial console servers
  • remote power control
  • network infrastructure
  • uninterruptible power supplies
  • shelving
  • cables
  • removable media

Understanding how all of those bits fit together to make a functioning LAVA instance is much easier when you use devices which are known to work in LAVA.

Early admin stuff:

  • recommendations on how to do admin:
    • start simple using our examples
    • build complexity slowly
    • only once you’re confident, start adding novel devices
  • where to find logs and debug information
  • device configuration and templates
  • getting a number of cheap ARMv7 development boards