confd+etcd+nginx 服务发现

https://learnku.com/articles/36229

https://www.chenshaowen.com/blog/service-discovery-etcd-confd-nginx.html

在进行应用部署时，服务运行起来后，通过接口向 Etcd 注册相关 key-value 信息，Confd 检测到 Etcd 的 key-value 变化后，立即触发程序通过模板形成新的 Nginx 配置文件。

Nginx 先做离线语法测试，如果没问题就覆盖原配置，进而 reload，测试不通过就不覆盖原配置，整个过程安全可控。

https://github.com/fanqingsong/docker-compose_confd_etcd_nginx

confd - docker-compose - etcd - nginx

Abstract

This practice follows confd - Quickstart Guide - Advanced Example.

docker-compose manages the following services:

etcd-server: key-value store, backend for confd

confd-nginx: nginx server managed by confd acording to the values inserted to etcd-server. Requests to localhost are routed to the python app

etcd-curl: inserts values to etcd-server via curl

py-app: simple python flask server, target of nginx proxy

etcd

https://etcd.io/

A distributed, reliable key-value store for the most critical data of a distributed system

What is etcd?

etcd is a strongly consistent, distributed key-value store that provides a reliable way to store data that needs to be accessed by a distributed system or cluster of machines. It gracefully handles leader elections during network partitions and can tolerate machine failure, even in the leader node. Learn more

https://learn.lianglianglee.com/%e4%b8%93%e6%a0%8f/etcd%e5%ae%9e%e6%88%98%e8%af%be/08%20Watch%ef%bc%9a%e5%a6%82%e4%bd%95%e9%ab%98%e6%95%88%e8%8e%b7%e5%8f%96%e6%95%b0%e6%8d%ae%e5%8f%98%e5%8c%96%e9%80%9a%e7%9f%a5%ef%bc%9f.md

第一，client获取事件的机制，etcd是使用轮询模式还是推送模式呢？两者各有什么优缺点？

第二，事件是如何存储的？会保留多久？watch命令中的版本号具有什么作用？

第三，当client和server端出现短暂网络波动等异常因素后，导致事件堆积时，server端会丢弃事件吗？若你监听的历史版本号server端不存在了，你的代码该如何处理？

第四，如果你创建了上万个watcher监听key变化，当server端收到一个写请求后，etcd是如何根据变化的key快速找到监听它的watcher呢？

接下来我就和你分别详细聊聊etcd Watch特性是如何解决这四大问题的。搞懂这四个问题，你就明白etcd甚至各类分布式存储Watch特性的核心实现原理了。

轮询 vs 流式推送

confd

https://github.com/kelseyhightower/confd

confd is a lightweight configuration management tool focused on:

keeping local configuration files up-to-date using data stored in etcd, consul, dynamodb, redis, vault, zookeeper, aws ssm parameter store or env vars and processing template resources.

reloading applications to pick up new config file changes

https://ops-doc.readthedocs.io/zh/latest/Linux_Notes/tools/confd-usage.html

使用来自 etcd 或 consul 的模板和数据管理本地应用程序配置文件。

confd是一个轻量级的配置管理工具，专注于：

使用存储在etcd、 consul、dynamodb、redis、 vault、zookeeper、aws ssm 参数存储或环境变量中的数据以及处理模板资源，使本地配置文件保持最新。

重新加载应用程序以获取新的配置文件更改