Connection Parameters conn_params

App developers can use conn_params in the submit.yml.erb to pass runtime data generated in the before.sh.erb back to the view.html.erb.

This is helpful for:

• Data that is only known after the job submits and starts running.

• Data that needs to be used to connect to the application.

This technique will generate a file in the app’s root called connection.yml when the app launches which will contain the defined variables and their associated values.

Configuration

The files which must be adjusted are:

my_app/
├── submit.html.erb
├── templates/
│   ├── before.sh.erb
└── view.html.erb

The files which can be adjusted to:

my_app/
├── submit.html.erb
├── templates/
│   ├── before.sh.erb
│   └── dir
│       └── another_script.sh.erb
└── view.html.erb

And the submit.yml.erb will use conn_params to set the custom variables to pass back to the view to be rendered:

---
batch_connect:
  template: "basic"
  conn_params:
    - custom_variable_one
    - custom_variable_two
    ...
...

Warning

The variables in before.sh.erb must be made available to the environment by using export.

Jupyter Notebook Example

Here’s an example using the bc_osc_jupypter app which needs information from the server to then pass on to the submission before it renders in the browser for the app’s launch card.

Within the template/before.sh.erb, observe the following lines:

JUPYTER_API="<%= context.jupyterlab_switch == "1" ? "lab" : "tree" %>"
...
export jupyter_api="$JUPYTER_API"

Now take this exported variable and include it in the submit.html.erb. Ensure that the syntax aligns with the following:

---
batch_connect:
  template: "basic"
  conn_params:
    - jupyter_api
...

In the view.html.erb, which renders after the submission in the interactive apps page, you can access the value of this variable with:

<%-
  ...
  next_url  = "#{base_url}/#{jupyter_api}"

  full_url="#{login_url}?next=#{CGI.escape(next_url)}"
  ...
%>

...

<form id="<%= form_id %>" action="<%= full_url %>" method="post" target="_blank" onsubmit="changeTarget()" >

This configuration uses the value from jupyter_api to populate the action attribute in the rendered page in the interactive sessions.