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hastexo XBlock: Makes arbitrarily complex lab environments available on an Open edX LMS

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hastexo XBlock

The hastexo XBlock is an Open edX API that integrates realistic lab environments into distributed computing courses. The hastexo XBlock allows students to access an OpenStack (or Google Cloud) environment within an edX course.

It leverages Apache Guacamole as a browser-based connection mechanism, which includes the ability to connect to graphical user environments (via VNC and RDP), in addition to terminals (via SSH).

Important changes in version 5

As of version 5, this XBlock uses a different interaction mechanism with Guacamole than it did in prior releases: rather than relying on a separately deployed Apache Tomcat servlet, it now uses the Daphne ASGI server.

If you follow the suggestions in this README, you will still be able to use the edx-configuration Ansible playbooks to deploy this XBlock to your Open edX instance, but we strongly suggest that you redeploy your Open edX frontend servers, rather than attempt to reconfigure them in-place.


The hastexo XBlock orchestrates a virtual environment (a "stack") that runs on a private or public cloud (currently OpenStack or Gcloud) using its orchestration engine. It provides a Secure Shell session directly within the courseware.

Stack creation is idempotent, so a fresh stack will be spun up only if it does not already exist. An idle stack will auto-suspend after a configurable time period, which is two minutes by default. The stack will resume automatically when the student returns to the lab environment.

Since public cloud environments typically charge by the minute to run virtual machines, the hastexo XBlock makes lab environments cost effective to deploy. The hastexo XBlock can run a fully distributed virtual lab environment for a course in Ceph, OpenStack, or Open vSwitch for approximately $25 per month on a public cloud (assuming students use the environment for 1 hour per day).

Course authors can fully define and customize the lab environment. It is only limited by the feature set of the cloud's deployment features.


The easiest way for platform administrators to deploy the hastexo XBlock and its dependencies to an Open edX installation is to pip install it to the edxapp virtualenv, and then to use the hastexo_xblock role included in the hastexo_xblock branch of edx/configuration.

To deploy the hastexo XBlock:

  1. Install it via pip:

    $ sudo /edx/bin/pip.edxapp install hastexo-xblock

    Do not run pip install with --upgrade, however, as this will break edx-platform's own dependencies.

  2. Collect static assets:

    $ sudo /edx/bin/edxapp-update-assets
  3. Add it to the ADDL_INSTALLED_APPS of your LMS environment, by editing /edx/app/edxapp/lms.env.json and adding:

  4. If you're going to use it in a content library, also add it to the ADVANCED_PROBLEM_TYPES of your Studio environment, by editing /edx/app/edxapp/cms.env.json and adding:

            "boilerplate_name": null,
            "component": "hastexo"
  5. This xblock uses a Django model to synchronize stack information across instances. Migrate the edxapp database so the hastexo_stack table is created:

    $ sudo /edx/bin/edxapp-migrate-lms
  6. Add configuration to XBLOCK_SETTINGS on /edx/app/edxapp/lms.env.json:

        "hastexo": {
            "terminal_url": "/hastexo-xblock/",
            "terminal_color_scheme": "white-black",
            "terminal_font_name": "monospace",
            "terminal_font_size": "10",
            "instructions_layout": "above",
            "launch_timeout": 900,
            "remote_exec_timeout": 300,
            "suspend_timeout": 120,
            "suspend_interval": 60,
            "suspend_concurrency": 4,
            "suspend_task_timeout": 900,
            "check_timeout": 120,
            "delete_interval": 86400,
            "delete_age": 14,
            "delete_attempts": 3,
            "delete_task_timeout": 900,
            "sleep_timeout": 10,
            "js_timeouts": {
                "status": 15000,
                "keepalive": 30000,
                "idle": 3600000,
                "check": 5000
            "providers": {
                "default": {
                    "type": "openstack",
                    "os_auth_url": "",
                    "os_auth_token": "",
                    "os_username": "",
                    "os_password": "",
                    "os_user_id": "",
                    "os_user_domain_id": "",
                    "os_user_domain_name": "",
                    "os_project_id": "",
                    "os_project_name": "",
                    "os_project_domain_id": "",
                    "os_project_domain_name": "",
                    "os_region_name": ""
                "provider2": {
                    "type": "gcloud",
                    "gc_type": "service_account",
                    "gc_project_id": "",
                    "gc_private_key_id": "",
                    "gc_private_key": "",
                    "gc_client_email": "",
                    "gc_client_id": "",
                    "gc_auth_uri": "",
                    "gc_token_uri": "",
                    "gc_auth_provider_x509_cert_url": "",
                    "gc_client_x509_cert_url": "",
                    "gc_region_id": ""
  7. Now install the Guacamole web app and stack supervisor scripts by cloning the hastexo_xblock fork of edx/configuration and assigning that role to the machine:

    $ git clone -b hastexo/juniper/hastexo_xblock
    $ cd edx-configuration/playbooks
    $ ansible-playbook -c local -i "localhost," run_role.yml -e role=hastexo_xblock
  8. At this point restart the LMS, the CMS, and the Celery workers, and also make sure the stack management jobs are running:

    sudo /edx/bin/supervisorctl restart lms:
    sudo /edx/bin/supervisorctl restart cms:
    sudo /edx/bin/supervisorctl restart edxapp_worker:
    sudo /edx/bin/supervisorctl start suspender:
    sudo /edx/bin/supervisorctl start reaper:
  9. Finally, in your course, go to the advanced settings and add the hastexo module to the "Advanced Module List" like so:


XBlock settings

The hastexo XBlock must be configured via XBLOCK_SETTINGS in lms.env.json, under the hastexo key. At the very minimum, you must configure a single "default" provider with the credentials specific to the cloud you will be using. All other variables can be left at their defaults.

This is a brief explanation of each:

  • terminal_url: URL to the Guacamole web app. If it is defined with a fully qualified domain, it must include the protocol (http:// or https://). If not, it is assumed to be an absolute path based on the current window.location. (It is possible to define it with a ":"-prefixed port, such as ":8080/hastexo-xblock/", for use in devstacks). (Default: /hastexo-xblock/)

  • terminal_color_scheme: Color scheme for the terminal window. Suitable values are described in Guacamole Documentation. For example, foreground:rgb:ff/ff/ff;background:rgb:00/00/00 and white-black both represent white text on a black background. (Default: white-black)

  • terminal_font_name: The name of the font to use in terminal. A matching font must be installed on the Guacamole server. (Default: monospace)

  • terminal_font_size: The size of the font to use in terminal, in points. (Default: 10)

  • instructions_layout: Configuration for instructions layout. It's possible to set the position for instructions to be 'above', 'below', 'left' or 'right' from the terminal window. (Default: above; this is currently an experimental feature)

  • launch_timeout: How long to wait for a stack to be launched, in seconds. (Default: 900)

  • remote_exec_timeout: How long to wait for a command to be executed remotely over SSH, in seconds. (Default: 300)

  • suspend_timeout: How long to wait before suspending a stack, after the last keepalive was received from the browser, in seconds. (Default: 120)

  • suspend_interval: The period between suspend job launches. (Default: 60)

  • suspend_concurrency: How many stacks to suspend on each job run. (Default: 4)

  • suspend_task_timeout: How long to wait for a stack to be suspended, in seconds. (Default: 900)

  • check_timeout: How long to wait before a check progress task fails. (Default: 120)

  • delete_age: Delete stacks that haven't been resumed in this many days. Set to 0 to disable. (Default: 14)

  • delete_interval: The period between reaper job launches. (Default: 3600)

  • delete_attempts: How many times to insist on deletion after a failure. (Default: 3)

  • delete_task_timeout: How long to wait for a stack to be deleted, in seconds. (Default: 900)

  • js_timeouts:

    • status: In the browser, when launching a stack, how long to wait between polling attempts until it is complete, in milliseconds (Default: 15000)

    • keepalive: In the browser, after the stack is ready, how long to wait between keepalives to the server, in milliseconds. (Default: 30000)

    • idle: In the browser, how long to wait until the user is considered idle, when no input is registered in the terminal, in milliseconds. (Default: 3600000)

    • check: In the browser, after clicking "Check Progress", how long to wait between polling attempts, in milliseconds. (Default: 5000)

  • providers: A dictionary of OpenStack providers that course authors can pick from. Each entry is itself a dictionary containing provider configuration parameters. You must configure at least one, named "default". The following is a list of supported parameters:

    • type: The provider type. Currently "openstack" or "gcloud". Defaults to "openstack" if not provided, for backwards-compatibility.

    The following apply to OpenStack only:

    • os_auth_url: OpenStack auth URL.

    • os_auth_token: OpenStack auth token.

    • os_username: OpenStack user name.

    • os_password: OpenStack password.

    • os_user_id: OpenStack user id.

    • os_user_domain_id: OpenStack domain id.

    • os_user_domain_name: OpenStack domain name.

    • os_project_id: OpenStack project id.

    • os_project_name: OpenStack project name.

    • os_project_domain_id: OpenStack project domain id.

    • os_project_domain_name: OpenStack project domain name.

    • os_region_name: OpenStack region name.

    The following apply to Gcloud only. All values aside from region can be obtained by creating a service account and downloading the JSON-format key:

    • gc_deploymentmanager_api_version: The deployment service api version. (Default: "v2")

    • gc_compute_api_version: The compute service api version. (Default: "v1")

    • gc_type: The type of account, currently only service_account.

    • gc_project_id: Gcloud project ID.

    • gc_private_key_id: Gcloud private key ID.

    • gc_private_key: Gcloud private key, in its entirety.

    • gc_client_email: Gcloud client email.

    • gc_client_id: Gcloud cliend ID.

    • gc_auth_uri: Gcloud auth URI.

    • gc_token_uri: Gcloud token URI.

    • gc_auth_provider_x509_cert_url: Gcloud auth provider cert URL.

    • gc_client_x509_cert_url: Gcloud client cert URL.

    • gc_region_id: Gcloud region where labs will be launched.

Creating an orchestration template for your course

To use the hastexo XBlock, start by creating an orchestration template and uploading it to the content store. The XBlock imposes some constraints on the template (detailed below), but you are otherwise free to customize your training environment as needed.

To ensure your template has the required configuration:

  1. Configure the template to accept a "run" parameter, which will contain information about the course run where the XBlock is instanced. This is intended to give course authors a way to, for example, tie this to a specific virtual image when launching VMs.

  2. If your orchestration engine allows it, configure the template to generate an SSH key pair dynamically and save the private key.

  3. In addition, if using RDP or VNC you must generate a random password and assign it to the stack user.

  4. Configure the template to have at least one instance that is publicly accessible via an IPv4 address.

  5. Provide the following outputs with these exact names:

    • public_ip: The publically accessible instance.

    • private_key: The generated passphrase-less SSH private key.

    • password: The generated password. (OPTIONAL)

    • reboot_on_resume: A list of servers to be rebooted upon resume. This is meant primarily as a workaround to resurrect servers that use nested KVM, as the latter does not support a managed save and subsequent restart. (OPTIONAL, DEPRECATED)

  6. Upload the template to the content store and make a note of its static asset file name.

Heat examples

A sample Heat template is provided under samples/hot/sample-template.yaml.

Accepting the run parameter:

  type: string
  description: Stack run

Generating an SSH key pair:

  type: OS::Nova::KeyPair
    name: { get_param: 'OS::stack_name' }
    save_private_key: true

Generating a random password and setting it:

  type: OS::Heat::RandomString
    length: 32

  type: OS::Heat::CloudConfig
            template: "user:{password}"
              "{password}": { get_resource: stack_password }

Defining the outputs:

    description: Floating IP address of deploy in public network
    value: { get_attr: [ deploy_floating_ip, floating_ip_address ] }
    description: Training private key
    value: { get_attr: [ training_key, private_key ] }
    description: Stack password
    value: { get_resource: stack_password }
    description: Servers to be rebooted after resume
      - { get_resource: server1 }
      - { get_resource: server2 }

Gcloud examples

A sample Gcloud template is provided under samples/gcloud/sample-template.yaml.jinja.

The Gcloud deployment manager cannot generate an SSH key or random password itself, so the XBlock will do it for you. There's no need to generate them or provide outputs manually. However, you do need to make use of the ones provided as properties:

  - name: {{ env["deployment"] }}-server
    type: compute.v1.instance
       - key: user-data
         value: |
             - default
             - name: training
               gecos: Training User
               groups: users,adm
                 - ssh-rsa {{ properties["public_key"] }}
               lock-passwd: false
               shell: /bin/false
               sudo: ALL=(ALL) NOPASSWD:ALL
             list: |
               training:{{ properties["password"] }}
         - echo "exec /usr/bin/screen -xRR" >> /home/training/.profile
         - echo {{ properties["private_key"] }} | base64 -d > /home/training/.ssh/id_rsa

Note that due to the fact that the deployment manager does not accept property values with multiple lines, the private key is base64-encoded.

As for outputs, in a Gcloud template one needs only one:

- name: public_ip
  value: $(ref.{{ env["deployment"] }}-server.networkInterfaces[0].accessConfigs[0].natIP)

Using the hastexo XBlock in a course

To create a stack for a student and display a terminal window where invoked, you need to define the hastexo tag in your course content. It must be configured with the following attributes:

  • stack_user_name: The name of the user that the Xblock will use to connect to the environment, as specified in the orchestration template.

  • protocol: One of 'ssh', 'rdp', or 'vnc'. This defines the protocol that will be used to connect to the environment. The default is 'ssh'.

The following are optional:

  • stack_template_path: The static asset path to the orchestration template, if not specified per provider below.

  • launch_timeout: How long to wait for a stack to be launched, in seconds. If unset, the global timeout will be used.

  • delete_age: Delete stacks that haven't been resumed in this many seconds. Overrides the globally defined setting. The global setting currently only supports days but will begin to support suffixes d, h, m, s in future releases. Using this attribute will allow setting the delete_age value per instance and configure it to have a shorter value.

  • read_only: Display a lab terminal in a read-only mode. If set to True, a lab stack will be created or resumed as usual, the student can see the lab terminal but is not able to interact with it. Default is False.

  • progress_check_label: Set a label for the progress check button. For example: Submit Answer or Check Progress (Default).

  • show_feedback: On progress check, show feedback on how many tasks out of total are completed. Default is True.

  • show_hints_on_error: On progress check failure, display the tests' standard error streams as hints. When show_feedback is set to False, hints will never be displayed and having this set to True will have no effect. Default is True.

  • progress_check_result_heading: Message to display on progress check result window. This could be set to "Answer Submitted" for example, when choosing to not display hints and feedback. Default is "Progress check result".

You can also use the following nested XML options:

  • providers: A list of references to providers configured in the platform. Each name attribute must match one of the providers in the XBlock configuration. capacity specifies how many environments should be launched in that provider at maximum (where "-1" means keep launching environments until encountering a launch failure, and "0" disables the provider). template is the content store path to the orchestration template (if not given, stack_template_path will be used). environment specifies a content store path to a either a Heat environment file, or, if using Gcloud, a YAML list of properties. If no providers are specified, the platform default will be used.

  • ports: A list of ports the user can manually choose to connect to. This is intended as a means of providing a way to connect directly to multiple VMs in a lab environment, via port forwarding or proxying at the VM with the public IP address. Each name attribute will be visible to the user. The number attribute specifies the corresponding port.

  • tests: A list of test scripts. The contents of each element will be run verbatim a a script in the user's lab environment, when they click the "Check Progress" button. As such, each script should define an interpreter via the "shebang" convention. If any scripts fail with a retval greater than 0, the learner gets a partial score for this instance of the XBlock. In this case, the stderr of failed scripts will be displayed to the learner as a list of hints on how to proceed.

For example, in XML:

<vertical url_name="lab_introduction">
  <hastexo xmlns:option=""
      - name: provider1
        capacity: 20
        template: hot_lab1_template.yaml
        environment: hot_lab1_env.yaml
      - name: provider2
        capacity: 30
        template: gcloud_lab1_template.yaml
        environment: gcloud_lab1_config.yaml
      - name: server1
        number: 3389
      - name: server2
        number: 3390
      - |
        # Check for login on vm1
        logins=$(ssh vm1 last root | grep root | wc -l)
        if [ $logins -lt 1 ]; then
          # Output a hint to stderr
          echo "You haven't logged in to vm1, yet." >&2
          exit 1
        exit 0
      - |
        # Check for file
        if [ ! -e ${file} ]; then
          # Output a hint to stderr
          echo "File \"${file}\" doesn't exist." >&2
          exit 1
        exit 0

Important: Do this only once per section. Defining it more than once per section is not supported.

Note on tests: as seen in the above example, it is recommended to wrap them all in <![CDATA[..]]> tags. This avoids XML parsing errors when special characters are encountered, such as the >&2 used to output to stderr in bash.

In order to add the hastexo Xblock through Studio, open the unit where you want it to go. Add a new component, select Advanced, then select the Lab component. This adds the XBlock. Edit the Settings as explained above.

Using the hastexo XBlock in a content library

This XBlock is usable in content libraries. It supports adding lab instructions as child blocks, so that when the block is randomized, the instructions are bundled together with it.

To add the XBlock to the library via Studio, make sure it is configured as one of the ADVANCED_PROBLEM_TYPES in cms.env.json, then select it as such when adding content to your library. (Note: as of Open edX Ironwood, the ability to do so requires running a patched version of edx-platform.)

The following child block types are currently supported:

* html
* video
* [pdf](

If using OLX, html blocks can be defined separately in the html subdirectory as usual, with the child element referring to it by URL name:

<vertical url_name="lab_introduction">
  <hastexo ...>
    <html url_name="lab_instructions">

Child blocks will always be rendered above the terminal.

Student experience

When students navigate to a unit with a hastexo XBlock in it, a new Heat stack will be created (or resumed) for them. The Heat stack will be as defined in the uploaded Heat template. It is unique per student and per course run. If the same tag appears on a different course, or different run of the same course, the student will get a different stack.

The stack will suspend if the student does not navigate to the hastexo unit in that section within the default two minutes (configurable via settings, as explained above). When the student gets to the hastexo unit, the stack will be resumed and they will be connected automatically and securely. They will not need a username, password, or host prompts to their personal lab environment. This happens transparently in the browser.

The student can work at their own pace in their environment. However, when a student closes the browser where the hastexo unit is displayed, or if they put their computer to sleep, a countdown is started. If the student does not reopen the environment within two minutes their stack will be suspended. When a student comes back to the lab environment to finish the exercise, their stack is resumed automatically. They are connected to the same training environment they were working with before, in the same state they left it in. (The process of suspension works just like in a home computer.)

Django admin page

To facilitate management of stack states without direct access to the database, a Django admin page is provided as a frontend for the hastexo_stack table. To access it, go to the following as a superuser:

The following features are currently implemented:

  • Searching: Search for a stack's name, course ID, status, and provider.

  • Filtering: On the filter tab to the right, it is possible to select from a preset list of three filters: course_id, status, and provider. The preset values are generated on the fly from existing records.

  • On-list editing: modify multiple stack's states or providers directly from the main list.

  • Marking stacks as deleted in bulk: to quickly change multiple stack states to DELETE_COMPLETE, and to reset their providers to "", select multiple stacks and use the "Mark selected stacks as DELETE_COMPLETE" action from the action dropdown.

  • Displaying owner's email: when opening a stack's edit form (by clicking on its name), the owner's email is displayed.

When changing providers, only the ones enabled by the author for the course in question are displayed. If none are present, then the list is expanded with the full set of providers configured in the platform.

The list of states is similarly limited to a known set of possibilities, but no further validation is made.

Furthermore, the following are not currently possible:

  • Displaying the owner's email on the main list

  • Searching for a stack owner's email

  • Adding a stack record

Note that making changes to the hastexo_stack table does not affect the stacks themselves. In other words, deleting an existing stack here will merely delete its database record: not only will the stack itself continue to exist, but the XBlock will cease to handle it automatically (such as suspending or deleting it) until such time as the learner relaunches it. The admin page is only offered as a convenient way to manually synchronize the database with actual stack states in case of failure. It should not be necessary to do so in day-to-day usage of the XBlock.

Usage in devstack

It is possible to use this XBlock in devstack. To do so, however, requires tweaking a few settings.

First, devstacks don't install nginx. Therefore, the Guacamole app is only reachable directly at its configured port. This means that terminal_url in the XBlock settings must be set to that port (by default, 8080):

    "hastexo": {
        "terminal_url": ":8080/hastexo-xblock/"

Next, open three terminal windows, and run each of the following concurrently:

paver devstack lms --settings=devstack_with_worker
./ lms celery worker --settings=devstack_with_worker -l DEBUG
./ lms --settings=devstack_with_worker suspender
./ lms --settings=devstack_with_worker reaper

Running tests

The testing framework is built on tox. After installing tox, you can simply run tox from your Git checkout of this repository.

In addition, you can run tox -r to throw away and rebuild the testing virtualenv, or tox -e flake8 to run only PEP-8 checks, as opposed to the full test suite.


This XBlock is licensed under the Affero GPL; see LICENSE for details.

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