零停机部署与热升级
通过滚动部署、健康检查以及 BEAM 的热代码升级能力，在不中断连接的情况下发布新的 Elixir 版本。
零停机部署与热升级 是 CoddyKit 上的免费 Elixir & Phoenix: Scalable Backend Development 课时。 这是第 4 节课，共 4 节。 你可以在下方免费阅读本课时的完整内容 — 然后在浏览器中使用内置代码编辑器和全天候 AI 导师进行实践。 这是 Elixir & Phoenix: Scalable Backend Development 学习路径的一部分，你的进度在网页和 CoddyKit 应用中同步。 Elixir & Phoenix: Scalable Backend Development 课程共包含 4 节课。
本课时的部分内容尚未翻译，以英文显示。
Why Zero Downtime Matters
Restarting a server drops in-flight requests and live WebSocket connections. Zero-downtime deploys roll out new code while users stay connected and unaware.
Two Strategies
The BEAM supports two upgrade paths:
- Rolling deploys: start new nodes, drain old ones — simple and common
- Hot code upgrades: swap code inside a running node without restart — powerful but complex
Rolling Deploys
A rolling deploy boots a new release alongside the old, shifts traffic over via a load balancer, then shuts the old one down. Most teams use this because it is straightforward and tooling-friendly.
Health Check Endpoints
Load balancers need to know when a new node is ready. Expose a lightweight health endpoint that returns 200 only when the app can serve traffic.
get "/healthz", HealthController, :check
# def check(conn, _), do: send_resp(conn, 200, "ok")Connection Draining
Before stopping an old node, stop accepting new requests but let active ones finish. This draining avoids cutting users off mid-request.
config :my_app, MyAppWeb.Endpoint,
drainer: [shutdown: 30_000]Database Migrations Safely
Old and new code run side by side during a rolling deploy, so migrations must be backward compatible. Add columns before using them; never rename or drop in a single deploy.
Hot Code Upgrades
The BEAM can replace a module's code in a live system. :code.load_file/1 loads the new version; running processes switch over on their next function call.
:code.purge(MyModule)
:code.load_file(MyModule)Appups and Relups
For full hot upgrades of a release, the BEAM uses appup files (per-application upgrade instructions) and relup files (release-level). Tools like Distillery could generate these.
code_change Callbacks
A long-lived GenServer can migrate its state during a hot upgrade via the code_change/3 callback, reshaping old state into the new format.
def code_change(_old_vsn, state, _extra) do
{:ok, Map.put(state, :version, 2)}
endTrade-offs
Hot upgrades avoid any restart but are hard to test and reason about. Most teams prefer rolling deploys for predictability, reserving hot upgrades for embedded or always-on telecom-style systems.
Rollback Plans
Always have a rollback ready:
- Keep the previous release artifact
- Make migrations reversible or additive only
- Automate rollback in your deploy pipeline
Quick Check
Test your zero-downtime knowledge.
Recap
You learned zero-downtime deployment:
- Rolling deploys drain old nodes while new ones serve
- Health checks tell the load balancer when a node is ready
- Migrations must be backward compatible
- Hot code upgrades swap code live via appup/relup and
code_change - Always keep a rollback plan
Users stay connected through every release.
常见问题解答
「零停机部署与热升级」课时是免费的吗？
是的 — 「零停机部署与热升级」的完整文本可在网页上免费阅读。要进行交互式练习（内置代码编辑器和全天候 AI 导师）并解锁 Elixir & Phoenix: Scalable Backend Development 课程的其余内容，请升级到 CoddyKit PRO。 Elixir & Phoenix: Scalable Backend Development 课程共包含 4 节课。
「零停机部署与热升级」这节课中我会学到什么？
通过滚动部署、健康检查以及 BEAM 的热代码升级能力，在不中断连接的情况下发布新的 Elixir 版本。 你通过在浏览器中直接运行的动手代码来练习 Elixir & Phoenix: Scalable Backend Development，全天候 AI 导师会在你学习这节课的过程中回答你的问题。
学习 Elixir & Phoenix: Scalable Backend Development 需要有经验吗？
无需任何先前经验。CoddyKit 上的 Elixir & Phoenix: Scalable Backend Development 课程适合初学者到高级学习者，你可以从这里开始或从头开始，按照自己的节奏学习。 这是第 4 节课，共 4 节。
「零停机部署与热升级」课时需要多长时间？
大多数 CoddyKit 课程大约需要 5–10 分钟。每节课都很精短且互动，所以你能稳步进步，并在网页和应用中从离开的地方继续。
我能在这节 Elixir & Phoenix: Scalable Backend Development 课中编写并运行代码吗？
能。每节 Elixir & Phoenix: Scalable Backend Development 课都包含内置代码编辑器，你可以在浏览器中直接编写并运行真实代码，并获得即时 AI 反馈 — 无需本地设置。