User Experience SLIs (next step)

Motivation

Continuing the work from User Experience SLIs, this addendum focus on the augmentation of the User Experience Framework by introducing a new service, the User Experience Tracker, that will add the capability of tracking User Experiences that never complete (due to errors mid journey), or do not complete within its expected lifetime.

This is being kept separate from the main blueprint for the reason that it is subject to change. The content presented here is aspirational only.

Scope

The User Experience Tracker is going to be responsible for the User Experience time out verification – especially relevant for tracking the asynchronous User Experience SLIs.

With the SDK consolidated, we can move and centralize the functionality of emitting events to this service, removing the complexity from the SDK.

The project will consist of:

1. User Experience SLI Tracker
2. LabKit SDK

Example:

flowchart LR
    User((User))

    subgraph ServiceA
        subgraph ProcessA
            LabKit
        end
    end
    subgraph ServiceB
        subgraph ProcessB
            LabKitB
        end
    end

    subgraph tracker[Tracker]
        missing_end[Missing end event]
        timeout_check{Timeout check}
        timeout_action[Timeout action]

        missing_end --> timeout_check
        timeout_check --No timeout--> missing_end
        timeout_check --Timeout reached--> timeout_action
    end

    User --Request--> ServiceA
    LabKit --Checkpoint--> tracker
    ServiceA --> ServiceB
    LabKitB --Checkpoint--> tracker

The project work items are scoped in the epic #1540.

User Experience SLI Tracker

• Centralized User Experience SLI state tracking
• Sensible time to live (TTL) threshold for User Experience duration
• State is stored and managed by Redis. Allowing the querying of stale User Experiences, timing out after configured threshold.
• Authentication
• Deployments:
  • Runway service for GitLab.com
  • Runway hosted service for Dedicated

It will serve an endpoint that will respond to the client generated payload:

A background process verifies all stale User Experience SLIs and clears them out, emitting failure events.

Components interactions given a synchronous User Experience:

sequenceDiagram
    participant User
    participant App as Service A
    participant AppB as Service B
    participant Tracker as User Experience Tracker
    participant Redis
    participant Event as Logs and Metrics

    User->>App: Request
    activate App

    App->>Tracker: Checkpoint 1
    Tracker->>Redis: Store Initial State
    Tracker->>Event: Emit Start Event
    Tracker-->>App: Response

    App->>AppB: Forward Request
    activate AppB

    AppB->>Tracker: Checkpoint 2
    Tracker->>Redis: Update State
    Tracker->>Event: Emit Intermediate Event
    Tracker-->>AppB: Response

    AppB-->>App: Response
    deactivate AppB

    App->>Tracker: Checkpoint 3
    Tracker->>Redis: Mark Complete
    Tracker->>Event: Emit Success Event
    Tracker-->>App: Response

    App-->>User: Response
    deactivate App

    loop Expired User Experience
        Tracker->>Redis: Check for Timeout
        alt Timeout Reached
            Tracker->>Redis: Mark Failed
            Tracker->>Event: Emit Failure Event
        end
    end

Components interactions given an asynchronous User Experience:

sequenceDiagram
    participant User
    participant Web as Web Service
    participant Worker
    participant Tracker as User Experience Tracker
    participant Redis
    participant Event as Logs and Metrics

    User->>Web: Request
    activate Web

    Web->>Tracker: Checkpoint 1
    Tracker->>Redis: Store Initial State
    Tracker->>Event: Emit Start Event
    Tracker-->>Web: Response

    Web->>Worker: Enqueue Job
    Web-->>User: Response
    deactivate Web

    Note over Worker: Job wait in queue

    Note over Worker: Job starts
    activate Worker
    Worker->>Tracker: Checkpoint 2
    Tracker->>Redis: Update State

    alt Success Case
        Worker->>Tracker: End User Experience (Success)
        Tracker->>Redis: Mark Complete
        Tracker->>Event: Emit Success Event
    else Failure Case
        Worker->>Tracker: End User Experience (Failed)
        Tracker->>Redis: Mark Failed
        Tracker->>Event: Emit Failure Event
    end

    Tracker-->>Worker: Response
    deactivate Worker

    loop Expired User Experiences
        Tracker->>Redis: Check for Missing End Events
        alt Timeout Reached
            Tracker->>Redis: Mark Failed
            Tracker->>Event: Emit Failure Event
        end
    end

Authentication

Authentication between the SDK and the User Experience SLI Tracker is required to prevent the sending of unexpected events that could distort the reliability metrics of GitLab features. E.g. the ai-gateway authentication and authorization.

SDK Requirements

• Trigger events towards the Tracker, instead of directly pushing events
• Automatic retries with exponential backoff for sending events to the User Experience SLI Tracker

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