slp-modular-cms/aidlc-docs/features/master-cms-module/construction/slave-availability-extension/functional-design/domain-entities.md

Domain Entities — Unit 2: slave-availability-extension

Entity Relationship Diagram

graph TD
    subgraph AvailabilityModule["Availability Module (slave side)"]
        DbCtx["AvailabilityDbContext"]
        MR["MasterRegistration\n(singleton row)"]
        Cache["MasterStatusCache\n(static fields)"]
        MAS["IMasterAvailabilityService\n/MasterAvailabilityService"]
    end

    DbCtx -->|owns| MR
    MAS -->|reads/writes| DbCtx
    MAS -->|updates| Cache
    MW["AvailabilityMiddleware\n(extended)"] -->|reads synchronously| Cache
    MC["MasterController\n(new)"] -->|delegates to| MAS

    classDef entity fill:#FFC107,stroke:#F57F17,color:#000
    classDef service fill:#9ae6b4,stroke:#2f855a,color:#000
    classDef infra fill:#63b3ed,stroke:#2b6cb0,color:#000
    classDef cache fill:#CE93D8,stroke:#6A1B9A,color:#000

    class MR entity
    class MAS service
    class DbCtx,MC infra
    class Cache,MW cache

Text alternative: AvailabilityDbContext owns the singleton MasterRegistration row. MasterAvailabilityService reads/writes the DbContext and updates the in-process MasterStatusCache (static fields). AvailabilityMiddleware reads the cache synchronously. MasterController delegates all logic to MasterAvailabilityService.

---

Entity: MasterRegistration

Singleton row — at most one record exists per slave instance. Upserted on each successful registration.

Field	Type	Constraints	Notes
Id	Guid	PK	Fixed value (e.g. Guid.Empty) enforces singleton
MasterUrl	string	Required, max 500	URL of the master CMS that registered this slave
ApiKey	string	Required, max 1000	Plain-text API key sent in first registration; used for subsequent validation
RegisteredAt	DateTimeOffset	Required	Timestamp of first registration
LastContactedAt	DateTimeOffset?	Optional	Updated on every successful master call (register, status push, get-url)

Singleton enforcement: The Id is a fixed known value (Guid.Parse("00000000-0000-0000-0000-000000000001")). On first POST /api/v1/master/register the row is created; on re-registration the same row is updated in-place. This avoids a composite unique constraint and makes EF upsert trivial.

---

In-Process Cache: MasterStatusCache (static fields)

Not a DB entity — lives in memory on the slave process.

Field	Type	Default	Notes
_masterIsAvailable	bool	true	Set by status push; true = pass gate
_masterDisableMessage	string?	null	Message forwarded from master to 503 response

No expiry (Q4=A): cache is valid indefinitely until the master pushes again. If the master goes offline permanently, the last known status is used. Default = true (Available) = fail-open.

---

DbContext: AvailabilityDbContext

New per-module DbContext in SlpModularCms.Modules.Availability. Separate from ApplicationDbContext (Core).

DbSet	Entity	Table Name
MasterRegistrations	MasterRegistration	AvailabilityMasterRegistrations

Migration assembly: SlpModularCms.Modules.Availability. Applied at startup in AvailabilityModule.UseModule.