[Alerting][Discuss] meta issue on mustache templating and action parameter processing

[pmuellr]

Our current story of having replaceable parameters in action parameters via mustache templates is not living up to the needs of our customers. Collecting some of the related issues here, want to noodle on this for a bit and we can come up with a plan for improvements.

• Alert simulation/preview #49411 - Alert simulation
• Ability to generate URLs in alert action parameters #49392 - Ability to generate URLs in alert action parameters
• Add image/chart support to actions #49908 - Add image/chart support to actions
• [Actions] Bi-directional action types #51636 - Bi-directional action types
• [Alerting] Validate action message in ActionForm for mustache compatibility #62928 - Validate action message in ActionForm for mustache compatibility
• [Alerting] support for watcher-like "dynamic attachments"  #64247 - support for watcher-like "dynamic attachments"
• [Alerting][Discuss] allow alerts to create default action parameters #66095 - allow alerts to create default action parameters
• [Alerting] Research alert summaries / bulk-able actions #68828 - Bulk/Un-bulkable alerts + standard fields
• [alerting] add doc about use of mustache double- and triple- braces in action parameters #70664 - add doc about use of mustache double- and triple- braces in action parameters
• Emails sent from Kibana Alerting to have a footer with a link back to the alert details #71243 - Emails sent from Kibana Alerting to have a footer with a link back to the alert details
• [Actions UI] Webhook action form with Body editor should support different HTTP body types, not only JSON #72202 - Webhook action form with Body editor should support different HTTP body types, not only JSON
• [Alerting] add a framework-provided mustache template variable that lists all the available variables and their values #75601 - add a framework-provided mustache template variable that lists all the available variables and their values
• Data formatting and manipulation support for Alert payloads #77793 - Data formatting and manipulation support for Alert payloads
• [Actions UI] Enable adding non quoted alert type variables in JSON body of action type #78877 - Enable adding non quoted alert type variables in JSON body of action type
• [Alerting UI] Add an option to being able to create a "sub-template" for a particular context variable. #78884 - Add an option to being able to create a "sub-template" for a particular context variable.
• [Alerts] unable to use a context variable with an embedded newline in a webhook action #79371 - unable to use a context variable with an embedded newline in a webhook action
• [Alerting UI] Extend JSON editor validation to check the context variable type #79789 - Extend JSON editor validation to check the context variable type
• [Actions] Ability to declare unescaped messageVariables #83780 - Ability to declare unescaped messageVariables
• [alerts][discuss] should alert types have a top-level action param variable for conditions #84148 - should alert types have a top-level action param variable for conditions
• [alerts] provide mustache functions for ease-of-use in transforming mustache variables #84217 - provide mustache functions for ease-of-use in transforming mustache variables
• [alerts] investigate usage of handlebars instead of mustache #84218 - investigate usage of handlebars instead of mustache

closed:

• add defaultActionMessage to index threshold alert UI type definition #78148 - add defaultActionMessage to index threshold alert UI type definition

[elasticmachine]

Pinging @elastic/kibana-alerting-services (Team:Alerting Services)

[pmuellr]

Looking at these with a view on priority:

#83780 - Ability to declare unescaped messageVariables

This one seems simple enough (haven't done a lot of research, but it's only UI, no server-side code), and has enough value I think we could try to squeeze this into 7.11.0

#66095 - allow alerts to create default action parameters

This one is probably going to be extremely useful, hopefully being able to provide a lot of the default templating we need across various actions, action groups, etc. I think the first iteration of this can be UI-side only, but long term we'll likely want this on the server as well.

Guessing it's too late at this stage for this to be useful in 7.11.0, as each alert will have to provide a function with default templates across many axes, for this to be useful. Feels like something we should get into master as soon as the 7.11 branch is cut though.

#84148 - should alert types have a top-level action param variable for conditions

I feel like this will have a lot of value as well, but also requires buy-in from all the alerts to be useful, and so is also not a great candidate for 7.11, but good one to start early for 7.12.