elsa-core/doc/wiki/http-scheduling-resilience.md

HTTP, Scheduling, And Resilience

HTTP, scheduling, and resilience are extension modules layered on top of workflow core, management, runtime, and expressions.

HTTP Module

Start in src/modules/Elsa.Http.

HttpFeature owns:

• inbound HTTP endpoint workflows
• outbound HTTP request activities
• route matching and route table updates
• HTTP bookmark payloads
• HTTP request/response content parsing and writing
• downloadable content handling
• file cache and zip management
• correlation and workflow instance ID selectors
• HTTP activity descriptors and UI hints
• HTTP resilience strategy registration
• HTTP ingress source registration for graceful shutdown

The public module extension is UseHttp.

Inbound HTTP Workflows

The inbound path is:

flowchart LR
    Request["ASP.NET request"] --> Middleware["HttpWorkflowsMiddleware"]
    Middleware --> RouteTable["IRouteTable / IRouteMatcher"]
    RouteTable --> Lookup["IHttpWorkflowLookupService"]
    Lookup --> Runtime["Workflow runtime"]
    Runtime --> Activity["HttpEndpoint activity"]
    Activity --> Response["HTTP response activity"]

Important files:

• HttpWorkflowsMiddleware
• HttpEndpoint
• HttpEndpointBase
• RouteMatcher
• RouteTable
• DefaultRouteTableUpdater
• HttpWorkflowLookupService

Hosts enable middleware with UseWorkflows.

Outbound HTTP

Outbound HTTP activities:

• SendHttpRequest
• FlowSendHttpRequest
• DownloadHttpFile

Supporting services include HttpClientFileDownloader, content factories, content parsers, and downloadable content handlers.

HTTP Security And Faults

HTTP endpoint authorization and faults are configurable through HttpFeature:

• AuthenticationBasedHttpEndpointAuthorizationHandler
• AllowAnonymousHttpEndpointAuthorizationHandler
• DefaultHttpEndpointFaultHandler
• DetailedHttpEndpointFaultHandler

The module registers authorization services because the authentication-based handler requires them.

HTTP Tests

Good test entry points:

• test/unit/Elsa.Http.UnitTests
• test/integration/Elsa.Http.IntegrationTests
• test/component/Elsa.Workflows.ComponentTests/Scenarios/Activities/Http
• test/component/Elsa.Workflows.ComponentTests/Scenarios/HttpWorkflows

Scheduling Module

Start in src/modules/Elsa.Scheduling.

SchedulingFeature registers:

• local scheduler
• cron parser
• trigger scheduler
• bookmark scheduler
• workflow scheduler
• tenant schedule updater
• create-schedules background task
• ScheduleWorkflows handlers
• Cron trigger payload validator
• scheduled-trigger ingress source for graceful shutdown
• scheduling activities through workflow management

The public extension is UseScheduling.

Scheduling Concepts

Scheduled workflows typically create trigger or bookmark payloads that the scheduler can wake later. Important files:

• Bookmarks
• Services
• Handlers
• StartupTasks
• TriggerPayloadValidators

The scheduler integrates with tenancy by reacting to tenant activation/deletion events.

Resilience Module

Start in src/modules/Elsa.Resilience and Elsa.Resilience.Core.

ResilienceFeature registers:

• activity descriptor modifier for resilient activities
• resilience strategy catalog
• strategy config evaluator
• resilient activity invoker
• configuration strategy source
• retry attempt recorders/readers
• transient exception detector and strategy
• FastEndpoints assembly for resilience descriptors/testing endpoints

HTTP registers HttpResilienceStrategy with resilience in HttpFeature.Configure().

Resilience Concepts

Core contracts:

• IResilienceStrategy
• IResilientActivity
• IResilientActivityInvoker
• IRetryAttemptRecorder
• ITransientExceptionDetector

Use resilience when an activity performs IO that can fail transiently. Keep strategy types registered by the owning module.

The resilience testing endpoint GET /elsa/api/simulate-response is included in the module. It requires exec:resilience:simulate-response (or wildcard exec:resilience or exec:*) and is intended for integration-testing resilience strategies, not for production traffic.

Cross-Cutting Graceful Shutdown

HTTP and Scheduling both register runtime ingress sources so graceful shutdown can pause new external work. When adding a new external event source, implement and register an IIngressSource in the owning module, then add runtime tests that prove pause/resume/drain behavior.