docs: architecture and system diagrams (#1973)

docs: architecture and system diagrams

Author: taddes

docs/src/SUMMARY.md

@@ -8,6 +8,7 @@
 [Introduction](introduction.md)
 [Application Configuration](config.md)
 [Docs and MdBook Notes](doc-notes.md)
+[Application Architecture](architecture.md)
 
 - [Tokenserver](tokenserver/tokenserver.md)
     - [Tokenserver API](tokenserver/tokenserver_api.md)

docs/src/architecture.md

@@ -0,0 +1,144 @@
+# Architecture
+
+A high-level architectural overview of the Sync Service which includes Sync and Tokenserver.
+
+## Syncstorage
+![image](assets/sync-architecture.png)
+
+Below is an illustration of a highly-simplified Sync flow:
+
+```mermaid
+graph LR
+
+  SignIn["Sign in to FxA"]
+  FxA[("FxA")]
+  OAuth["Sync client gets OAuth token"]
+  PresentToken["OAuth Token presented to Tokenserver"]
+  Tokenserver[("Tokenserver")]
+  AssignNode["Tokenserver assigns storage node"]
+  InfoCollections["info/collections: Do we even need to sync?"]
+
+  MetaGlobal["meta/global: Do we need to start over?"]
+  CryptoKeys["crypto/keys: Get keys"]
+
+  GetStorage["GET storage/<collection>: Fetch new data"]
+  PostStorage["POST storage/<collection>: Upload new data"]
+
+  %% Main flow
+  SignIn --> FxA
+  FxA --> OAuth 
+  OAuth --> PresentToken
+  PresentToken --> Tokenserver
+  Tokenserver --> AssignNode
+  AssignNode --> InfoCollections
+
+  %% Decision / metadata path
+  InfoCollections --> MetaGlobal
+  MetaGlobal --> CryptoKeys
+
+  %% Sync operations
+  CryptoKeys --> GetStorage
+  CryptoKeys --> PostStorage
+```
+
+### Storage-Client Relationship
+
+This high-level diagram illustrates the standard Sync collections and their relationships.
+
+```mermaid
+graph TD
+
+  %% ===== Storage =====
+  DB[("DB")]
+  BookmarksMirror[("Bookmarks Mirror")]
+  LoginStorage[("Login Manager Storage")]
+  AutofillStorage[("Form Autofill Storage")]
+  XPIDB[("XPI Database")]
+  CredentialStorage[("Credential Storage")]
+
+  %% ===== Client components =====
+  Places["Places"]
+  LoginManager["Login Manager"]
+  TabbedBrowser["Tabbed Browser"]
+  AddonManager["Add-on Manager"]
+  ExtensionBridge["Extension Storage Bridge"]
+
+  %% ===== Sync engines =====
+  Bookmarks["Bookmarks"]
+  History["History"]
+  Passwords["Passwords"]
+
+  CreditCards["Credit cards"]
+  Addresses["Addresses"]
+  OpenTabs["Open tabs"]
+
+  Addons["Add-ons"]
+  Clients["Clients"]
+
+  %% ===== Sync internals =====
+  subgraph Sync["Sync"]
+  HTTPClient["HTTP Client"]
+  TokenClient["Tokenserver Client"]
+  end
+
+  %% ===== Storage =====
+  SyncStorage[("Sync Storage Server")]
+  TokenServer[("Tokenserver")]
+  PushService["Push Service"]
+
+  subgraph FirefoxAccounts["Firefox Accounts Service"]
+  PushIntegration["Push Integration"]
+  FxAHTTP["HTTP Clients"]
+  end
+  subgraph Accounts
+  MozillaPush[("Mozilla Push Server")]
+  FxAAuth[("FxA Auth Server")]
+  FxAOAuth[("FxA OAuth Server")]
+  FxAProfile[("FxA Profile Server")]
+  end
+
+  %% ===== Relationships =====
+  DB --> Places
+  BookmarksMirror --> Places
+  Places --> Bookmarks
+  Places --> History
+  LoginStorage <--> LoginManager
+
+  AutofillStorage --> CreditCards
+  AutofillStorage --> Addresses
+
+  TabbedBrowser --> OpenTabs
+  AddonManager --> Addons
+  XPIDB --> AddonManager
+  ExtensionBridge --> Clients
+
+  %% ===== Sync engine / Collections =====
+  Bookmarks --> Sync
+  History --> Sync
+  Passwords --> Sync
+  CreditCards --> Sync
+  Addresses --> Sync
+  OpenTabs --> Sync
+  Addons --> Sync
+  Clients --> Sync
+  HTTPClient --> Sync
+  TokenClient <--> TokenServer
+  SyncStorage <--> HTTPClient
+
+  %% ===== Push & Accounts =====
+  FirefoxAccounts --> PushIntegration
+  FirefoxAccounts --> FxAHTTP
+  FxAAuth <--> MozillaPush
+
+  PushIntegration --> PushService
+  FxAHTTP --> FxAAuth
+  FxAHTTP --> FxAOAuth
+  FxAHTTP --> FxAProfile
+  CredentialStorage --> FirefoxAccounts
+```
+
+## Tokenserver
+![image](assets/tokenserver-architecture.png)
+
+The intent of this file is inspired by a very sensible [blog post](https://matklad.github.io/2021/02/06/ARCHITECTURE.md.html) many developers are familiar with regarding the necessity to illustrate systems with clarity. Given Sync's complexity and interrelationships with other architectures, this 
+