Erlang OTP: Distributed & Fault-Tolerant Systems Programming · 课时

发布版本管理与部署

了解在生产环境中管理发布版本、部署更新和执行回滚的最佳实践。

发布版本管理与部署 是 CoddyKit 上的免费 Erlang OTP: Distributed & Fault-Tolerant Systems Programming 课时。这是第 3 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 Erlang OTP: Distributed & Fault-Tolerant Systems Programming 学习路径的一部分，你的进度在网页和 CoddyKit 应用中同步。 Erlang OTP: Distributed & Fault-Tolerant Systems Programming 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 Version Your Releases?

When you build an Erlang application for production, it's bundled into a release. Just like any software, releases need clear version numbers.

Versioning helps you:

Track changes over time.
Identify specific builds.
Manage compatibility with other systems.
Plan for upgrades and rollbacks.

Erlang's Versioning System

In Erlang, versioning happens at different levels. Each individual application (an .app file) has its own version. The overall release (the .rel file) also has a version that typically reflects the entire bundle.

The vsn key in an .app file defines an application's version.

% my_app.app file (conceptual)
{application, my_app,
 [{description, "My Erlang Application"},
  {vsn, "1.0.0"},
  {modules, [my_app_app, my_app_sup]},
  {registered, []},
  {applications, [kernel, stdlib]},
  {mod, {my_app_app, []}},
  {env, []}]}.

Semantic Versioning (SemVer)

A widely adopted standard is Semantic Versioning (SemVer), typically formatted as MAJOR.MINOR.PATCH. It's a great practice to follow for your Erlang applications.

MAJOR: Incremented for incompatible API changes.
MINOR: Incremented for new functionality in a backward-compatible way.
PATCH: Incremented for backward-compatible bug fixes.

This helps users understand the impact of an upgrade.

Applying SemVer in Erlang

You'll typically apply SemVer to your application's vsn in the .app file. When you create a release, its version (relvsn) often matches the main application's version or follows a similar scheme.

Tools like rebar3 manage these versions when building releases.

% my_app.app file
{application, my_app,
 [{description, "My Erlang Service"},
  {vsn, "1.2.3"},
  {modules, [my_app_app, my_app_sup]},
  {registered, []},
  {applications, [kernel, stdlib]},
  {mod, {my_app_app, []}},
  {env, []}]}.

Deployment Strategies Overview

Once you have a versioned Erlang release, how do you get it running in production? There are several strategies, depending on your system's requirements for uptime and complexity.

Cold Deployment: Simplest, involves downtime.
Hot Upgrades: Zero-downtime (covered in previous lesson).
Blue/Green or Canary Deployments: More advanced, often used with orchestration tools.

Cold Deployment: Simple Restart

A cold deployment is the most straightforward method. You stop your currently running Erlang system completely, replace its files with the new release, and then start the new version.

This method always incurs downtime, making it suitable for systems where brief interruptions are acceptable.

# Stop the old release
/path/to/my_app/bin/my_app stop

# (Replace files with new release)

# Start the new release
/path/to/my_app/bin/my_app start

Hot Upgrades vs. Full Deployment

Recall from the previous lesson that hot code loading allows you to upgrade a running Erlang system without stopping it.

While powerful for applying patches or minor feature additions, hot upgrades are specific to changing *parts* of a running system. A full deployment often refers to the initial setup or a complete replacement of the entire release, sometimes involving a cold restart or more advanced traffic management.

The Importance of Rollbacks

Even with careful testing, new deployments can introduce unexpected issues. A robust deployment strategy always includes a plan for rollbacks.

A rollback means reverting your system to a previous, stable version if the new deployment fails or causes problems. This minimizes the impact of failures and restores service quickly.

Erlang's Rollback Mechanism

Erlang releases are designed to support rollbacks. When you perform a hot upgrade, Erlang generates an .relup script that describes how to move between versions. Crucially, it also knows how to reverse that script to go back.

Even with cold deployments, you can switch back to a previous release by managing your release directories and restarting the desired version.

# Example of a rollback command using release_handler
# This would typically be part of a custom script or release tool

% release_handler:install_release("my_app-1.1.0").
% release_handler:make_permanent("my_app-1.1.0").

# Alternatively, for cold deployment:
# /path/to/my_app_1.1.0/bin/my_app start

Test Your Understanding

Order the steps for a typical cold deployment of an Erlang release.

Summary: Versioning & Deployment

You've learned about the critical aspects of release versioning and deployment in Erlang:

Versioning: Use vsn in .app files, ideally following SemVer (MAJOR.MINOR.PATCH), to track and manage changes.
Deployment: Understand cold deployment (with downtime) and its distinction from hot upgrades.
Rollbacks: Always plan for reverting to a stable previous version to ensure system resilience.

These practices are key to managing robust Erlang applications in production!

常见问题解答

「发布版本管理与部署」课时是免费的吗？

是的 — 「发布版本管理与部署」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 Erlang OTP: Distributed & Fault-Tolerant Systems Programming 课程的其余内容，请升级到 CoddyKit PRO。 Erlang OTP: Distributed & Fault-Tolerant Systems Programming 课程共包含 4 节课。

「发布版本管理与部署」这节课中我会学到什么？

了解在生产环境中管理发布版本、部署更新和执行回滚的最佳实践。你通过在浏览器中直接运行的动手代码来练习 Erlang OTP: Distributed & Fault-Tolerant Systems Programming，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 Erlang OTP: Distributed & Fault-Tolerant Systems Programming 需要有经验吗？

无需任何先前经验。CoddyKit 上的 Erlang OTP: Distributed & Fault-Tolerant Systems Programming 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 3 节课，共 4 节。

「发布版本管理与部署」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 Erlang OTP: Distributed & Fault-Tolerant Systems Programming 课中编写并运行代码吗？

能。每节 Erlang OTP: Distributed & Fault-Tolerant Systems Programming 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。

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