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Architecture — msp-httpbin-operator

This document describes the architecture of the HttpBin MSP example.

Overview

flowchart TB
    subgraph kcp["kcp (control plane)"]
        subgraph provider["Provider Workspace<br/>root:msp:httpbin-provider"]
            APIExport["APIExport<br/>api-syncagent"]
        end
        subgraph consumer["Consumer Workspace<br/>root:msp:customer-a"]
            APIBinding["APIBinding<br/>→ api-syncagent"]
            HttpBinOrder["HttpBin<br/>httpbin-demo"]
        end
    end

    subgraph kind["kind cluster (service cluster)"]
        subgraph kcpsystem["kcp-system namespace"]
            SyncAgent["api-syncagent<br/>(deployment)"]
        end
        subgraph httpbinsystem["httpbin-system namespace"]
            Operator["httpbin-operator<br/>(deployment)"]
        end
        subgraph default["default namespace"]
            HttpBinCR["HttpBin CR<br/>(synced)"]
            Deploy["Deployment<br/>httpbin-demo"]
            Service["Service<br/>httpbin-demo"]
            Pod["Pod<br/>kennethreitz/httpbin"]
        end
    end

    %% Relationships
    APIBinding -->|binds to| APIExport
    HttpBinOrder -->|"sync DOWN"| SyncAgent
    SyncAgent -->|creates| HttpBinCR
    HttpBinCR -->|watched by| Operator
    Operator -->|creates| Deploy
    Operator -->|creates| Service
    Deploy -->|runs| Pod
    Service -->|exposes| Pod
    HttpBinCR -->|"sync UP (status)"| SyncAgent
    SyncAgent -->|updates| HttpBinOrder

    style kcp fill:#e1f5fe
    style kind fill:#fff3e0
    style HttpBinOrder fill:#c8e6c9
    style HttpBinCR fill:#c8e6c9
Loading

Flow

  1. Consumer orders an HttpBin — The consumer creates an HttpBin CR in their kcp workspace (root:msp:customer-a).

  2. api-syncagent syncs DOWN — The agent (running in kind) watches the consumer workspace via the APIBinding. When it sees the new HttpBin, it creates a corresponding HttpBin CR in the kind cluster.

  3. httpbin-operator provisions resources — The operator (running in kind) watches for HttpBin CRs. When it sees one, it creates:

    • A Deployment running the kennethreitz/httpbin container
    • A Service exposing the deployment

  4. Status syncs UP — The operator updates the HttpBin CR's .status (ready, url). The api-syncagent syncs this status back to the consumer's HttpBin in kcp.

  5. Consumer sees ready state — The consumer can now see their HttpBin is ready and get the service URL.

Components

Component Location Purpose
kcp Host process Control plane — hosts workspaces, APIExports, APIBindings
api-syncagent kind / kcp-system Syncs objects between kcp workspaces and the kind cluster
httpbin-operator kind / httpbin-system Watches HttpBin CRs, creates Deployments + Services
HttpBin CRD kind Defines the HttpBin custom resource

Key Differences from msp-postgres-kcp-only

Aspect msp-postgres-kcp-only msp-httpbin-operator
Backing operator CloudNativePG (third-party) Custom httpbin-operator
API passthrough CNPG's native Cluster API Custom HttpBin API
Related resources Connection Secret syncs back No related resources
Complexity Higher (stateful database) Lower (stateless httpbin)