feat(config): integrate etcd-based configuration management

- Add etcd-client dependency with TLS support
- Implement EtcdConfig struct for reading config values with priority: etcd > env > default
- Add ServiceRegistry for service discovery registration in etcd
- Create from_etcd method in AppConfig for loading SMTP configuration
- Update main.rs to use etcd-based config loading with fallback mechanism
- Add etcd module with client connection and key-value operations
- Modify Dockerfile to use cargo-chef for faster builds
- Add docker-compose.yaml for emailks service deployment
- Include AGENTS.md with development guidelines and best practices
- Add build.sh script for podman-based container building
- Update dependencies in Cargo.toml and Cargo.lock

AGENTS.md

@@ -0,0 +1,182 @@
+# AGENTS.md — 开发规范 / Development Guidelines
+
+> 本文件为所有 AI 编码助手（Claude Code、pi、Cursor 等）提供统一的开发指导。
+> This file provides unified development guidelines for all AI coding assistants.
+
+**最后更新 / Last Updated**: 2026-06-11
+
+---
+
+## 1. 语言 / Language
+
+**Always respond in Chinese (中文).** Use the user's language for all conversations and explanations. Code, commands, and technical terms can remain in English.
+
+始终使用中文回复。代码、命令和技术术语可以保留英文。
+
+---
+
+## 2. 代码风格 / Code Style
+
+### 2.1 基本原则 / Basic Principles
+
+| 规则 / Rule | 说明 / Description |
+|-----------|-------------------|
+| 遵循现有风格 | Follow existing project conventions |
+| 有意义命名 | Use meaningful variable names |
+| 函数长度 | Keep functions under **50 lines** |
+| 嵌套深度 | Maximum nesting depth: **3 levels** |
+| 注释 | Add comments for complex logic only |
+
+### 2.2 Rust 最佳实践 / Rust Best Practices
+
+| 规则 / Rule | 说明 / Description |
+|-----------|-------------------|
+| 错误传播 | Use `?` operator; never use `unwrap()` in non-test code |
+| `unsafe` | Avoid; if necessary, add `// SAFETY:` comment |
+| `clone()` | Minimize usage; prefer references |
+| 魔法数字 | No magic numbers; use named constants |
+| 硬编码字符串 | No hardcoded strings; use enums or constants |
+
+### 2.3 导入规范 / Import Guidelines
+
+```rust
+// 标准库 → 第三方 crate → 本地模块
+use std::collections::HashMap;
+
+use serde::{Deserialize, Serialize};
+
+use crate::error::{AppError, AppResult};
+```
+
+---
+
+## 3. 禁止模式 / Forbidden Patterns
+
+以下代码模式在项目中严格禁止：
+
+| 禁止项 / Forbidden | 说明 / Reason |
+|-------------------|--------------|
+| `// ── xxxx ──────────` | 禁止使用此类分隔线注释 |
+| `unwrap()` / `expect()` (非测试) | 使用 `?` 或安全替代 |
+| `panic!()` / `unreachable!()` | 使用错误类型替代 |
+| 未处理的 `todo!()` | 必须有对应的 issue 追踪 |
+| 注释掉的代码 | 使用 Git 历史追溯 |
+| 过深嵌套 (≥4层) | 使用 early return 扁平化逻辑 |
+| 过长函数 (>50行) | 拆分为更小的函数 |
+| 魔法数字 | 使用 `const` 定义命名常量 |
+| 硬编码字符串 | 使用枚举或常量 |
+
+---
+
+## 4. 错误处理 / Error Handling
+
+### 4.1 错误处理原则
+
+| 原则 / Principle | 说明 / Description |
+|----------------|-------------------|
+| 显式处理 | Handle all errors explicitly; no silent failures |
+| 用户友好 | Internal errors are logged; user-facing messages should be helpful |
+| 错误上下文 | Use `.context()` or `.map_err()` to add context |
+
+### 4.2 错误日志格式
+
+```rust
+tracing::error!(
+    error = %err,
+    operation = "operation_name",
+    "Failed to perform operation"
+);
+```
+
+---
+
+## 5. 安全规范 / Security
+
+| 规则 / Rule | 说明 / Description |
+|-----------|-------------------|
+| 密钥管理 | Never hardcode secrets or API keys |
+| 输入验证 | Always validate and sanitize user input |
+| SMTP 安全 | Use TLS for SMTP connections |
+| 密码安全 | Use proper hashing (Argon2, bcrypt) |
+
+---
+
+## 6. 工作流程 / Workflow
+
+### 6.1 开发流程
+
+1. **理解先于编写** — Read before write; understand context first
+2. **最小变更** — Minimal changes; don't refactor unrelated code
+3. **验证变更** — Verify after changes; run tests or check output
+
+### 6.2 AI 助手工作规范
+
+| 规则 / Rule | 说明 / Description |
+|-----------|-------------------|
+| 先读后写 | Always read existing code before making changes |
+| 最小侵入 | Make minimal changes |
+| 验证结果 | Run `cargo check` or `cargo test` after changes |
+| 解释变更 | Explain what you changed and why |
+
+### 6.3 常用命令 / Common Commands
+
+```bash
+cargo build                      # 构建 / Build
+cargo check                      # 快速检查 / Quick check
+cargo test                       # 运行测试 / Run tests
+cargo clippy                     # Lint 检查 / Lint checks
+cargo fmt                        # 格式化 / Format code
+```
+
+---
+
+## 7. Git 规范 / Git Workflow
+
+### 7.1 提交信息格式
+
+```
+<type>(<scope>): <subject>
+
+[optional body]
+
+[optional footer]
+```
+
+| Type | 说明 / Description |
+|------|-------------------|
+| `feat` | 新功能 / New feature |
+| `fix` | Bug 修复 / Bug fix |
+| `refactor` | 重构 / Code refactoring |
+| `docs` | 文档 / Documentation |
+| `test` | 测试 / Tests |
+| `chore` | 构建/工具 / Build/tooling |
+
+### 7.2 提交原则
+
+| 原则 / Principle | 说明 / Description |
+|----------------|-------------------|
+| 原子提交 | Each commit should address one concern |
+| 完整性 | Each commit should leave the codebase in a working state |
+| 禁止强制推送 | Never force push to main branch |
+
+---
+
+## 附录 / Appendix
+
+### 项目架构速查 / Quick Architecture Reference
+
+```
+emailks — 邮件发送服务 / Email Sending Service
+
+email.rs       → 邮件发送核心 / Email sending core
+server.rs      → gRPC 服务 / gRPC server
+queue.rs       → 邮件队化 / Email queue
+status.rs      → 状态管理 / Status management
+error.rs       → 错误类型 / Error types
+config.rs      → 配置管理 / Configuration
+proto/         → Protobuf 定义 / Protobuf definitions
+```
+
+---
+
+*This document is maintained by the development team. For questions or suggestions, please open an issue.*

Cargo.lock

@@ -89,6 +89,12 @@ version = "2.13.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "b4388bee8683e3d04af747c73422af53102d2bd24d9eadb6cbc100baef4b43f8"
 
+[[package]]
+name = "bumpalo"
+version = "3.20.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "72f5acc6cb2ba439de613abc23857ec3d78374d8ed5ac84e9d11336e87da8649"
+
 [[package]]
 name = "bytes"
 version = "1.11.1"
@@ -171,9 +177,12 @@ name = "emailks"
 version = "0.1.0"
 dependencies = [
  "dotenvy",
+ "etcd-client",
  "lettre",
  "prost",
  "prost-types",
+ "serde",
+ "serde_json",
  "tokio",
  "tokio-stream",
  "tonic",
@@ -182,6 +191,7 @@ dependencies = [
  "tonic-prost-build",
  "tracing",
  "tracing-subscriber",
+ "uuid",
 ]
 
 [[package]]
@@ -197,7 +207,25 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "39cab71617ae0d63f51a36d69f866391735b51691dbda63cf6f96d042b63efeb"
 dependencies = [
  "libc",
- "windows-sys",
+ "windows-sys 0.61.2",
+]
+
+[[package]]
+name = "etcd-client"
+version = "0.18.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "5ed900ba953ca6bf1fadb75e0c6b73d8463b9e2bb6bdb7b4573e8e7295852fbe"
+dependencies = [
+ "http",
+ "prost",
+ "tokio",
+ "tokio-stream",
+ "tonic",
+ "tonic-build",
+ "tonic-prost",
+ "tonic-prost-build",
+ "tower",
+ "tower-service",
 ]
 
 [[package]]
@@ -301,6 +329,17 @@ dependencies = [
  "slab",
 ]
 
+[[package]]
+name = "getrandom"
+version = "0.2.17"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "ff2abc00be7fca6ebc474524697ae276ad847ad0a6b3faa4bcb027e9a4614ad0"
+dependencies = [
+ "cfg-if",
+ "libc",
+ "wasi",
+]
+
 [[package]]
 name = "getrandom"
 version = "0.4.2"
@@ -601,6 +640,17 @@ version = "1.0.18"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "8f42a60cbdf9a97f5d2305f08a87dc4e09308d1276d28c869c684d7777685682"
 
+[[package]]
+name = "js-sys"
+version = "0.3.100"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f2025f20d7a4fa7785846e7b63d10a76d3f1cee98ee5cb79ea59703f95e42162"
+dependencies = [
+ "cfg-if",
+ "futures-util",
+ "wasm-bindgen",
+]
+
 [[package]]
 name = "lazy_static"
 version = "1.5.0"
@@ -699,7 +749,7 @@ checksum = "02bd0af71c67b473010cbbc60715ee815645a4dc942899111f494b4b737d6fda"
 dependencies = [
  "libc",
  "wasi",
- "windows-sys",
+ "windows-sys 0.61.2",
 ]
 
 [[package]]
@@ -740,7 +790,7 @@ version = "0.50.3"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "7957b9740744892f114936ab4a57b3f487491bbeafaf8083688b16841a4240e5"
 dependencies = [
- "windows-sys",
+ "windows-sys 0.61.2",
 ]
 
 [[package]]
@@ -992,6 +1042,20 @@ version = "0.8.10"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "dc897dd8d9e8bd1ed8cdad82b5966c3e0ecae09fb1907d58efaa013543185d0a"
 
+[[package]]
+name = "ring"
+version = "0.17.14"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "a4689e6c2294d81e88dc6261c768b63bc4fcdb852be6d1352498b114f61383b7"
+dependencies = [
+ "cc",
+ "cfg-if",
+ "getrandom 0.2.17",
+ "libc",
+ "untrusted",
+ "windows-sys 0.52.0",
+]
+
 [[package]]
 name = "rustix"
 version = "1.1.4"
@@ -1002,16 +1066,57 @@ dependencies = [
  "errno",
  "libc",
  "linux-raw-sys",
- "windows-sys",
+ "windows-sys 0.61.2",
 ]
 
+[[package]]
+name = "rustls"
+version = "0.23.40"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "ef86cd5876211988985292b91c96a8f2d298df24e75989a43a3c73f2d4d8168b"
+dependencies = [
+ "log",
+ "once_cell",
+ "ring",
+ "rustls-pki-types",
+ "rustls-webpki",
+ "subtle",
+ "zeroize",
+]
+
+[[package]]
+name = "rustls-pki-types"
+version = "1.14.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "30a7197ae7eb376e574fe940d068c30fe0462554a3ddbe4eca7838e049c937a9"
+dependencies = [
+ "zeroize",
+]
+
+[[package]]
+name = "rustls-webpki"
+version = "0.103.13"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "61c429a8649f110dddef65e2a5ad240f747e85f7758a6bccc7e5777bd33f756e"
+dependencies = [
+ "ring",
+ "rustls-pki-types",
+ "untrusted",
+]
+
+[[package]]
+name = "rustversion"
+version = "1.0.22"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "b39cdef0fa800fc44525c84ccb54a029961a8215f9619753635a9c0d2538d46d"
+
 [[package]]
 name = "schannel"
 version = "0.1.29"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "91c1b7e4904c873ef0710c1f407dde2e6287de2bebc1bbbf7d430bb7cbffd939"
 dependencies = [
- "windows-sys",
+ "windows-sys 0.61.2",
 ]
 
 [[package]]
@@ -1050,6 +1155,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "9a8e94ea7f378bd32cbbd37198a4a91436180c5bb472411e48b5ec2e2124ae9e"
 dependencies = [
  "serde_core",
+ "serde_derive",
 ]
 
 [[package]]
@@ -1129,7 +1235,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "52d1cfed4120b4d927bf7c0f86d2087a4a7d6027c906d9f9d525a80573b9be51"
 dependencies = [
  "libc",
- "windows-sys",
+ "windows-sys 0.61.2",
 ]
 
 [[package]]
@@ -1138,6 +1244,12 @@ version = "1.2.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "6ce2be8dc25455e1f91df71bfa12ad37d7af1092ae736f3a6cd0e37bc7810596"
 
+[[package]]
+name = "subtle"
+version = "2.6.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "13c2bddecc57b384dee18652358fb23172facb8a2c51ccc10d74c157bdea3292"
+
 [[package]]
 name = "syn"
 version = "2.0.117"
@@ -1173,10 +1285,10 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "32497e9a4c7b38532efcdebeef879707aa9f794296a4f0244f6f69e9bc8574bd"
 dependencies = [
  "fastrand",
- "getrandom",
+ "getrandom 0.4.2",
  "once_cell",
  "rustix",
- "windows-sys",
+ "windows-sys 0.61.2",
 ]
 
 [[package]]
@@ -1211,7 +1323,7 @@ dependencies = [
  "signal-hook-registry",
  "socket2",
  "tokio-macros",
- "windows-sys",
+ "windows-sys 0.61.2",
 ]
 
 [[package]]
@@ -1235,6 +1347,16 @@ dependencies = [
  "tokio",
 ]
 
+[[package]]
+name = "tokio-rustls"
+version = "0.26.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "1729aa945f29d91ba541258c8df89027d5792d85a8841fb65e8bf0f4ede4ef61"
+dependencies = [
+ "rustls",
+ "tokio",
+]
+
 [[package]]
 name = "tokio-stream"
 version = "0.1.18"
@@ -1282,6 +1404,7 @@ dependencies = [
  "socket2",
  "sync_wrapper",
  "tokio",
+ "tokio-rustls",
  "tokio-stream",
  "tower",
  "tower-layer",
@@ -1457,6 +1580,12 @@ version = "0.2.6"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "ebc1c04c71510c7f702b52b7c350734c9ff1295c464a03335b00bb84fc54f853"
 
+[[package]]
+name = "untrusted"
+version = "0.9.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "8ecb6da28b8a351d773b68d5825ac39017e680750f980f3a1a85cd8dd28a47c1"
+
 [[package]]
 name = "url"
 version = "2.5.8"
@@ -1475,6 +1604,17 @@ version = "1.0.4"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "b6c140620e7ffbb22c2dee59cafe6084a59b5ffc27a8859a5f0d494b5d52b6be"
 
+[[package]]
+name = "uuid"
+version = "1.23.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "144d6b123cef80b301b8f72a9e2ca4370ddec21950d0a103dd22c437006d2db7"
+dependencies = [
+ "getrandom 0.4.2",
+ "js-sys",
+ "wasm-bindgen",
+]
+
 [[package]]
 name = "valuable"
 version = "0.1.1"
@@ -1520,6 +1660,51 @@ dependencies = [
  "wit-bindgen 0.51.0",
 ]
 
+[[package]]
+name = "wasm-bindgen"
+version = "0.2.123"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "a254a4b10c19a76f09a27640e7ffbf9bc30bf67e16a3bf28aaefa4920fe81563"
+dependencies = [
+ "cfg-if",
+ "once_cell",
+ "rustversion",
+ "wasm-bindgen-macro",
+ "wasm-bindgen-shared",
+]
+
+[[package]]
+name = "wasm-bindgen-macro"
+version = "0.2.123"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "24a40fc75b0ec6f3746ceb10d36f53a93dcd68a93b11b6445983945d79eba0dc"
+dependencies = [
+ "quote",
+ "wasm-bindgen-macro-support",
+]
+
+[[package]]
+name = "wasm-bindgen-macro-support"
+version = "0.2.123"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "908f34bd9b9ce3d4caf07b72dfab63d61504d156856c6bd3cd87fa350cf3985b"
+dependencies = [
+ "bumpalo",
+ "proc-macro2",
+ "quote",
+ "syn",
+ "wasm-bindgen-shared",
+]
+
+[[package]]
+name = "wasm-bindgen-shared"
+version = "0.2.123"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "7acbf7616c27b194bbb550bf77ed0c2c3e5b7fd1260a93082b95fb7f47959b92"
+dependencies = [
+ "unicode-ident",
+]
+
 [[package]]
 name = "wasm-encoder"
 version = "0.244.0"
@@ -1560,6 +1745,15 @@ version = "0.2.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "f0805222e57f7521d6a62e36fa9163bc891acd422f971defe97d64e70d0a4fe5"
 
+[[package]]
+name = "windows-sys"
+version = "0.52.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "282be5f36a8ce781fad8c8ae18fa3f9beff57ec1b52cb3de0789201425d9a33d"
+dependencies = [
+ "windows-targets",
+]
+
 [[package]]
 name = "windows-sys"
 version = "0.61.2"
@@ -1569,6 +1763,70 @@ dependencies = [
  "windows-link",
 ]
 
+[[package]]
+name = "windows-targets"
+version = "0.52.6"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "9b724f72796e036ab90c1021d4780d4d3d648aca59e491e6b98e725b84e99973"
+dependencies = [
+ "windows_aarch64_gnullvm",
+ "windows_aarch64_msvc",
+ "windows_i686_gnu",
+ "windows_i686_gnullvm",
+ "windows_i686_msvc",
+ "windows_x86_64_gnu",
+ "windows_x86_64_gnullvm",
+ "windows_x86_64_msvc",
+]
+
+[[package]]
+name = "windows_aarch64_gnullvm"
+version = "0.52.6"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "32a4622180e7a0ec044bb555404c800bc9fd9ec262ec147edd5989ccd0c02cd3"
+
+[[package]]
+name = "windows_aarch64_msvc"
+version = "0.52.6"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "09ec2a7bb152e2252b53fa7803150007879548bc709c039df7627cabbd05d469"
+
+[[package]]
+name = "windows_i686_gnu"
+version = "0.52.6"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "8e9b5ad5ab802e97eb8e295ac6720e509ee4c243f69d781394014ebfe8bbfa0b"
+
+[[package]]
+name = "windows_i686_gnullvm"
+version = "0.52.6"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "0eee52d38c090b3caa76c563b86c3a4bd71ef1a819287c19d586d7334ae8ed66"
+
+[[package]]
+name = "windows_i686_msvc"
+version = "0.52.6"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "240948bc05c5e7c6dabba28bf89d89ffce3e303022809e73deaefe4f6ec56c66"
+
+[[package]]
+name = "windows_x86_64_gnu"
+version = "0.52.6"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "147a5c80aabfbf0c7d901cb5895d1de30ef2907eb21fbbab29ca94c5b08b1a78"
+
+[[package]]
+name = "windows_x86_64_gnullvm"
+version = "0.52.6"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "24d5b23dc417412679681396f2b49f3de8c1473deb516bd34410872eff51ed0d"
+
+[[package]]
+name = "windows_x86_64_msvc"
+version = "0.52.6"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "589f6da84c646204747d1270a2a5661ea66ed1cced2631d546fdfb155959f9ec"
+
 [[package]]
 name = "wit-bindgen"
 version = "0.51.0"
@@ -1713,6 +1971,12 @@ dependencies = [
  "synstructure",
 ]
 
+[[package]]
+name = "zeroize"
+version = "1.8.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "b97154e67e32c85465826e8bcc1c59429aaaf107c1e4a9e53c8d8ccd5eff88d0"
+
 [[package]]
 name = "zerotrie"
 version = "0.2.4"

Cargo.toml

@@ -12,9 +12,12 @@ name = "emailks"
 path = "main.rs"
 [dependencies]
 dotenvy = "0.15"
+etcd-client = { version = "0.18", features = ["tls"] }
 lettre = { version = "0.11", features = ["tokio1-native-tls"] }
 prost = "0.14"
 prost-types = "0.14"
+serde = { version = "1", features = ["derive"] }
+serde_json = "1"
 tokio = { version = "1", features = ["rt-multi-thread", "macros", "sync", "signal"] }
 tokio-stream = { version = "0.1", features = ["sync"] }
 tonic = "0.14"
@@ -22,6 +25,7 @@ tonic-health = "0.14"
 tonic-prost = "0.14"
 tracing = "0.1"
 tracing-subscriber = { version = "0.3", features = ["env-filter"] }
+uuid = { version = "1", features = ["v7"] }
 
 [build-dependencies]
 tonic-prost-build = "0.14"

Dockerfile

@@ -1,38 +1,33 @@
-# ---- builder ----
+FROM rust:1.96-bookworm AS chef
-FROM rust:1.96-slim-bookworm AS builder
+RUN apt-get update && \
-
+    apt-get install -y --no-install-recommends \
-RUN apt-get update && apt-get install -y --no-install-recommends \
+        protobuf-compiler libprotobuf-dev \
-    pkg-config \
+        pkg-config libssl-dev \
-    libssl-dev \
+        mold clang && \
-    protobuf-compiler \
+    rm -rf /var/lib/apt/lists/*
-    && rm -rf /var/lib/apt/lists/*
+RUN cargo install cargo-chef
-
 WORKDIR /app
 
-# Cache dependencies
+FROM chef AS planner
-COPY Cargo.toml Cargo.lock ./
+COPY . .
-COPY build.rs ./
+RUN cargo chef prepare --recipe-path recipe.json
-COPY proto/ proto/
-RUN echo '' >lib.rs && \
-    echo 'fn main() {}' >main.rs && \
-    cargo build --release --bin emailks; \
-    rm -f lib.rs main.rs
 
-# Build real binary
+FROM chef AS builder
+COPY --from=planner /app/recipe.json recipe.json
+RUN cargo chef cook --release --recipe-path recipe.json
 COPY . .
 RUN cargo build --release --bin emailks && \
-    cp target/release/emailks /app/emailks
+    strip target/release/emailks
 
-# ---- runtime ----
+FROM ubuntu:26.04
-FROM debian:bookworm-slim
+RUN apt-get update && \
+    apt-get install -y --no-install-recommends \
+        ca-certificates libssl3 && \
+    rm -rf /var/lib/apt/lists/*
+COPY --from=builder /app/target/release/emailks /usr/local/bin/emailks
 
-RUN apt-get update && apt-get install -y --no-install-recommends \
+ENV EMAILKS_HOST=0.0.0.0
-    ca-certificates \
+ENV EMAILKS_PORT=50051
-    libssl3 \
-    && rm -rf /var/lib/apt/lists/*
-
-COPY --from=builder /app/emailks /usr/local/bin/emailks
 
 EXPOSE 50051
-
 ENTRYPOINT ["emailks"]

build.sh

@@ -0,0 +1,3 @@
+#/bin/bash
+
+podman build --network=host --build-arg http_proxy= --build-arg https_proxy= -t emailks .

config.rs

@@ -54,6 +54,43 @@ pub enum SmtpTls {
 }
 
 impl AppConfig {
+    pub fn from_etcd(
+        host: String, port: u16, username: String, password: String,
+        from_email: String, from_name: String, reply_to: String,
+        tls: String, timeout_secs: u64, helo_name: String, allow_request_from: bool,
+        queue_capacity: Option<usize>,
+        listen_addr_str: &str,
+    ) -> Result<Self, ConfigError> {
+        let tls = match tls.trim().to_ascii_lowercase().as_str() {
+            "none" | "false" | "0" => SmtpTls::None,
+            "starttls" | "start_tls" | "start-tls" => SmtpTls::StartTls,
+            "tls" | "ssl" | "smtps" => SmtpTls::Tls,
+            _ => SmtpTls::StartTls,
+        };
+
+        validate_port("PORT", port)?;
+
+        Ok(Self {
+            smtp: SmtpConfig {
+                host,
+                port,
+                username: if username.is_empty() { None } else { Some(username) },
+                password: if password.is_empty() { None } else { Some(password) },
+                from_email: if from_email.is_empty() { None } else { Some(from_email) },
+                from_name: if from_name.is_empty() { None } else { Some(from_name) },
+                reply_to: if reply_to.is_empty() { None } else { Some(reply_to) },
+                tls,
+                timeout: std::time::Duration::from_secs(timeout_secs),
+                helo_name: if helo_name.is_empty() { None } else { Some(helo_name) },
+                allow_request_from,
+            },
+            queue_capacity,
+            listen_addr: listen_addr_str
+                .parse::<std::net::SocketAddr>()
+                .map_err(|e: std::net::AddrParseError| ConfigError::InvalidEnv { name: "LISTEN_ADDR", reason: e.to_string() })?,
+        })
+    }
+
     pub fn from_env() -> Result<Self, ConfigError> {
         let _ = dotenvy::dotenv();
 

docker-compose.yaml

@@ -0,0 +1,14 @@
+x-emailks: &emailks
+  image: emailks
+  restart: unless-stopped
+  env_file: .env
+  environment:
+    RUST_LOG: info
+    APP_SMTP_LISTEN_ADDR: 0.0.0.0:50050
+    APP_SMTP_QUEUE_CAPACITY: "1000"
+
+services:
+  emailks:
+    <<: *emailks
+    ports:
+      - "50050:50050"

etcd.rs

@@ -0,0 +1,163 @@
+use etcd_client::{Client, PutOptions};
+use std::sync::Arc;
+use tokio::sync::Mutex;
+
+/// etcd-backed config reader. Priority: etcd > env var > default.
+pub struct EtcdConfig {
+    client: Arc<Mutex<Client>>,
+    prefix: String,
+}
+
+impl EtcdConfig {
+    pub async fn connect(endpoints: Vec<String>, prefix: &str) -> Result<Self, String> {
+        let client = Client::connect(endpoints, None)
+            .await
+            .map_err(|e| format!("etcd connect: {e}"))?;
+        Ok(Self { client: Arc::new(Mutex::new(client)), prefix: prefix.to_string() })
+    }
+
+    /// Get config value. Checks etcd first, then env var, then default.
+    pub async fn get(&self, key: &str, default: &str) -> String {
+        tracing::info!(key, "etcd get config");
+        // 1. Try etcd
+        let etcd_key = format!("{}config/{}", self.prefix, key);
+        if let Ok(mut client) = self.client.try_lock() {
+            if let Ok(resp) = client.get(etcd_key.as_str(), None).await {
+                if let Some(kv) = resp.kvs().first() {
+                    if let Ok(v) = kv.value_str() {
+                        if !v.is_empty() {
+                            tracing::info!(key, value = v, "config from etcd");
+                            return v.to_string();
+                        }
+                    }
+                }
+            }
+        }
+        // 2. Try env var
+        if let Ok(v) = std::env::var(key) {
+            if !v.is_empty() {
+                tracing::info!(key, value = %v, "config from env");
+                return v;
+            }
+        }
+        // 3. Default
+        tracing::info!(key, value = %default, "config default");
+        default.to_string()
+    }
+
+    /// Get and parse config value.
+    pub async fn get_parsed<T: std::str::FromStr>(&self, key: &str, default: T) -> T
+    where
+        T::Err: std::fmt::Display,
+        T: std::fmt::Display,
+    {
+        let default_str = default.to_string();
+        let s = self.get(key, &default_str).await;
+        s.parse().unwrap_or(default)
+    }
+
+    /// Set config value in etcd for other services to read.
+    pub async fn set(&self, key: &str, value: &str) -> Result<(), String> {
+        let etcd_key = format!("{}config/{}", self.prefix, key);
+        let mut client = self.client.lock().await;
+        client
+            .put(etcd_key, value, None)
+            .await
+            .map_err(|e| format!("etcd put: {e}"))?;
+        Ok(())
+    }
+
+    /// Get the underlying etcd client for use by ServiceRegistry.
+    pub fn client(&self) -> Arc<Mutex<Client>> {
+        self.client.clone()
+    }
+
+    /// Get the etcd key prefix.
+    pub fn prefix(&self) -> &str {
+        &self.prefix
+    }
+}
+
+/// Register this service instance in etcd with a lease.
+pub struct ServiceRegistry {
+    client: Arc<Mutex<Client>>,
+    prefix: String,
+}
+
+impl ServiceRegistry {
+    pub fn new(client: Arc<Mutex<Client>>, prefix: &str) -> Self {
+        Self { client, prefix: prefix.to_string() }
+    }
+
+    /// Register this service under /{prefix}/services/{service_name}/{instance_id}
+    pub async fn register(&self, service_name: &str, addr: &str) -> Result<(), String> {
+        let instance_id = uuid::Uuid::now_v7().to_string();
+        let addr = addr.to_string();
+        let key = format!("{}services/{}/{}", self.prefix, service_name, instance_id);
+
+        let instance = serde_json::json!({
+            "addr": &addr,
+            "port": 0,
+            "version": env!("CARGO_PKG_VERSION"),
+        });
+        let value = serde_json::to_string(&instance).map_err(|e| format!("json: {e}"))?;
+
+        let lease = {
+            let mut client = self.client.lock().await;
+            client
+                .lease_grant(15, None)
+                .await
+                .map_err(|e| format!("lease: {e}"))?
+        };
+
+        {
+            let mut client = self.client.lock().await;
+            let opts = PutOptions::new().with_lease(lease.id());
+            client
+                .put(key.clone(), value, Some(opts))
+                .await
+                .map_err(|e| format!("put: {e}"))?;
+        }
+
+        tracing::info!(service = service_name, instance = %instance_id, addr, "registered in etcd");
+
+        // Spawn keep-alive
+        let c = self.client.clone();
+        tokio::spawn(async move {
+            loop {
+                let result = {
+                    let mut client = c.lock().await;
+                    client.lease_keep_alive(lease.id()).await
+                };
+                match result {
+                    Ok((_keeper, mut stream)) => {
+                        use tokio_stream::StreamExt;
+                        while stream.next().await.is_some() {}
+                    }
+                    Err(e) => tracing::warn!(lease_id = lease.id(), error = %e, "keepalive failed"),
+                }
+                tokio::time::sleep(std::time::Duration::from_secs(5)).await;
+                // Re-grant and re-register
+                let new_lease = {
+                    let mut client = c.lock().await;
+                    client.lease_grant(15, None).await
+                };
+                if let Ok(lease_resp) = new_lease {
+                    let new_id = lease_resp.id();
+                    let instance = serde_json::json!({
+                        "addr": addr,
+                        "port": 0,
+                        "version": env!("CARGO_PKG_VERSION"),
+                    });
+                    if let Ok(v) = serde_json::to_string(&instance) {
+                        let mut client = c.lock().await;
+                        let opts = PutOptions::new().with_lease(new_id);
+                        let _ = client.put(key.clone(), v, Some(opts)).await;
+                    }
+                }
+            }
+        });
+
+        Ok(())
+    }
+}

lib.rs

@@ -2,6 +2,7 @@ pub mod config;
 pub mod email;
 pub mod email_build;
 pub mod error;
+pub mod etcd;
 pub mod queue;
 pub mod server;
 pub mod status;

main.rs

@@ -1,6 +1,7 @@
 use emailks::{
-    config::AppConfig, email::EmailSender, pb::email::v1::email_service_server::EmailServiceServer,
+    config::AppConfig, email::EmailSender, etcd::{EtcdConfig, ServiceRegistry},
-    queue::EmailQueue, server::EmailServiceImpl,
+    pb::email::v1::email_service_server::EmailServiceServer, queue::EmailQueue,
+    server::EmailServiceImpl,
 };
 use tonic::transport::Server;
 use tracing::{error, info};
@@ -11,18 +12,66 @@ const DEFAULT_QUEUE_CAPACITY: usize = 1_000;
 async fn main() -> Result<(), Box<dyn std::error::Error>> {
     tracing_subscriber::fmt()
         .with_env_filter(
-            tracing_subscriber::EnvFilter::try_from_default_env().unwrap_or_else(|_| "info".into()),
+            tracing_subscriber::EnvFilter::try_from_default_env()
+                .unwrap_or_else(|_| "info".into()),
         )
         .init();
 
-    let config = AppConfig::from_env()?;
+    dotenvy::dotenv().ok();
-    info!(?config.smtp.host, port = config.smtp.port, "smtp config loaded");
+
+    // Phase 1: read etcd endpoints from env (required to bootstrap etcd)
+    let etcd_endpoints: Vec<String> = std::env::var("ETCD_ENDPOINTS")
+        .unwrap_or_else(|_| "http://localhost:2379".to_string())
+        .split(',')
+        .map(|s| s.trim().to_string())
+        .filter(|s| !s.is_empty())
+        .collect();
+    let etcd_prefix = std::env::var("ETCD_KEY_PREFIX")
+        .unwrap_or_else(|_| "/appks/".to_string());
+
+    // Phase 2: connect etcd, create config overlay (etcd > env > default)
+    let etcd = EtcdConfig::connect(etcd_endpoints, &etcd_prefix).await?;
+    let listen_addr_str = etcd.get("EMAILKS_LISTEN_ADDR", "127.0.0.1:50051").await;
+
+    // Phase 3: register this service so other services (appks) can discover us
+    let registry = ServiceRegistry::new(etcd.client(), &etcd_prefix);
+    registry.register("emailks", &listen_addr_str).await?;
+
+    // Phase 4: load SMTP config — each key: etcd first, then env, then default
+    let smtp_host = etcd.get("APP_SMTP_HOST", "").await;
+    if smtp_host.is_empty() {
+        return Err("APP_SMTP_HOST is required (set via etcd or env)".into());
+    }
+    let smtp_port: u16 = etcd.get_parsed("APP_SMTP_PORT", 587u16).await;
+    let smtp_from_email = etcd.get("APP_SMTP_FROM_EMAIL", "").await;
+    let smtp_from_name = etcd.get("APP_SMTP_FROM_NAME", "EmailKS").await;
+    let smtp_reply_to = etcd.get("APP_SMTP_REPLY_TO", "").await;
+    let smtp_tls = etcd.get("APP_SMTP_TLS", "starttls").await;
+    let smtp_timeout_secs: u64 = etcd.get_parsed("APP_SMTP_TIMEOUT_SECS", 30u64).await;
+    let smtp_allow_request_from: bool = etcd.get_parsed("APP_SMTP_ALLOW_REQUEST_FROM", false).await;
+    let smtp_username = etcd.get("APP_SMTP_USERNAME", "").await;
+    let smtp_password = etcd.get("APP_SMTP_PASSWORD", "").await;
+    let smtp_helo_name = etcd.get("APP_SMTP_HELO_NAME", "").await;
+
+    let queue_capacity: Option<usize> = {
+        let s = etcd.get("APP_SMTP_QUEUE_CAPACITY", "").await;
+        if s.is_empty() { None } else { s.parse().ok() }
+    };
+
+    let config = AppConfig::from_etcd(
+        smtp_host, smtp_port, smtp_username, smtp_password,
+        smtp_from_email, smtp_from_name, smtp_reply_to,
+        smtp_tls, smtp_timeout_secs, smtp_helo_name, smtp_allow_request_from,
+        queue_capacity,
+        &listen_addr_str,
+    )?;
+
+    info!(host = %config.smtp.host, port = config.smtp.port, "smtp config loaded (etcd priority)");
 
     let sender = EmailSender::new(config.smtp)?;
     let (queue, worker) = match config.queue_capacity {
-        // `Some(0)` explicitly opts into an unbounded queue (mainly for testing).
         Some(0) => {
-            info!("creating unbounded queue by explicit configuration");
+            info!("creating unbounded queue");
             EmailQueue::unbounded()
         }
         Some(cap) => {
@@ -30,10 +79,7 @@ async fn main() -> Result<(), Box<dyn std::error::Error>> {
             EmailQueue::bounded(cap)
         }
         None => {
-            info!(
+            info!(capacity = DEFAULT_QUEUE_CAPACITY, "creating bounded queue (default)");
-                capacity = DEFAULT_QUEUE_CAPACITY,
-                "creating bounded queue with default capacity"
-            );
             EmailQueue::bounded(DEFAULT_QUEUE_CAPACITY)
         }
     };
@@ -60,7 +106,6 @@ async fn main() -> Result<(), Box<dyn std::error::Error>> {
         .await?;
 
     info!("server stopped");
-
     if let Err(e) = worker_handle.await {
         tracing::error!(error = %e, "worker task panicked");
     }
@@ -70,7 +115,7 @@ async fn main() -> Result<(), Box<dyn std::error::Error>> {
 
 async fn shutdown_signal() {
     match tokio::signal::ctrl_c().await {
-        Ok(()) => info!("shutdown signal received, draining..."),
+        Ok(()) => info!("shutdown signal received"),
-        Err(err) => error!(%err, "failed to install CTRL+C handler, shutting down"),
+        Err(err) => error!(%err, "failed to install CTRL+C handler"),
     }
 }