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

pip install hastexo-xblock==7.11.0


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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).

Version compatibility matrix

You must install a supported release of this XBlock to match the Open edX and Tutor version you are deploying. If you are installing this plugin from a branch in this Git repository, you must select the appropriate one:

Open edX release Tutor version XBlock version XBlock branch
Maple >=13.2, <14 >=6.0, <7.0 stable-6.0
Nutmeg >=14.0, <15 >=7.0 master
Olive >=15.0, <16 >=7.5 master
Palm >=16.0, <17 >=7.5 master
Quince >=17.0, <18 >=7.9 master

Instructions for deploying this XBlock with Tutor can be found below, in the Deployment with Tutor section.


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.

Deployment with Tutor

Running this XBlock with Tutor (for Open edX Maple and later) requires two steps:

  1. Install the XBlock to your Tutor environment by adding it to the OPENEDX_EXTRA_PIP_REQUIREMENTS list in config.yml:

      - "hastexo-xblock==7.11.0"

    For additional information, please refer to the official documentation.

  2. Install and enable the tutor-contrib-hastexo plugin:

    pip install git+https://github.com/hastexo/tutor-contrib-hastexo
    tutor plugins enable hastexo

    Add the necessary configurations to your Tutor config.yml. Unless you want to change the default configurations, you'll only need to add the settings for the XBlock via HASTEXO_XBLOCK_SETTINGS, for example:

      check_timeout: 120
      delete_age: 0
      delete_attempts: 3
      delete_interval: 3600
      delete_task_timeout: 900
      guacamole_js_version: 1.5.4
      enable_fullscreen: false
      instructions_layout: above
        check: 5000
        idle: 3600000
        keepalive: 30000
        status: 15000
      launch_timeout: 900
          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: ""
          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: ""
      remote_exec_timeout: 300
      sleep_timeout: 10
      suspend_concurrency: 4
      suspend_interval: 60
      suspend_task_timeout: 900
      suspend_timeout: 120
      terminal_color_scheme: white-black
      terminal_font_name: monospace
      terminal_font_size: '10'
      terminal_url: /hastexo-xblock/

    For more details about each setting, please refer to the XBlock settings section below.

  3. Before deploying services with Tutor, build the Docker image for the hastexo service, and also build a custom openedx image:

    tutor images build openedx hastexo

    For more information about the plugin configuration, please refer to the plugin README.

  4. After you have deployed Open edX with Tutor, your platform is operational, and you have created a course in Open edX Studio, go to Settings → Advanced Settings and add the hastexo module to Advanced Module List, like so:


XBlock settings

The hastexo XBlock must be configured via XBLOCK_SETTINGS in lms.env.json (or lms.yml), 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)

  • enable_fullscreen: An option to allow learners to launch a lab in fullsceen mode, in a separate browser window. (Default: false)

  • lab_usage_limit: Allocate limited time per user for labs across the platform, in seconds. (Default is None, meaning there is no time limit).

  • lab_usage_limit_breach_policy: What to do when the learner's lab limit has been exceeded.

    • None (the default) means just write a message to the logs.

    • warn will display a warning to the learner that the limit has been reached, but does allow them to keep using the labs.

    • block blocks the learner's access to the lab.

  • 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.

The following are optional:

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

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

  • stack_key_type: An SSH key type for accessing the lab environment. Options are rsa, ed25519 and "" (default). If a key type is chosen, a key with the selected type will be generated for the lab environment. If set to an empty string, the key handling should be done via the lab template.

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

  • suspend_timeout: Timeout for how long to wait before suspending a stack, after the last keepalive was received from the browser, in seconds. Takes precedence over the globally defined timeout."

  • 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.

  • hidden: An option to hide the lab itself in the browser while spinning up the lab environment in the background. Default is False.

  • enable_fullscreen: An option to allow learners to launch a lab in fullsceen mode, in a separate browser window. If used, overrides the globally defined setting. Options are "true", "false" and "inherit". Default is "inherit" (to use global value).

  • 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="http://code.edx.org/xblock/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](https://github.com/MarCnu/pdfXBlock)

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.)

Copy & paste

Within the text terminal, learners can use copy and paste by marking up text with the left mouse button, and then using right-click or middle-click to paste.

Within the graphical (RDP) terminal, so long as the terminal has focus (normally meaning that the learner has left-clicked into it once), learners can use any copy and paste facility that the desktop provides. This includes the Ctrl‑C/Ctrl‑V key combinations, and middle mouse clicks.

Copy & paste to and from the lab environment (i.e. from the terminal to the learner's browser, or vice versa) is also possible, though some considerations apply.

Pasting into the lab environment requires two transitions, because we are dealing with two clipboards (one for the browser and one for the lab environment). Thus, the learner must

  1. Copy something into their clipboard on their client.
  2. Left-click into the terminal.
  3. Hit Ctrl‑V. (This is the first transition, which populates the terminal's clipboard.)
  4. Right-click, middle-click, or type Ctrl‑Shift‑V in the terminal. (This is the second transition, which pastes from the terminal's clipboard.)

Copying out from the lab environment is more direct, though at this time it works only on Mozilla Firefox (support in other browsers may follow). To copy from their terminal into their local clipboard, the learner must

  1. Mark up some text in their terminal.
  2. Switch to another application window on their client.
  3. Hit Ctrl‑V.

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.

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.