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Translating by Firstadream
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Rapid prototyping with docker-compose
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========================================
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In this write-up we'll look at a Node.js prototype for **finding stock of the Raspberry PI Zero** from three major outlets in the UK.
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I wrote the code and deployed it to an Ubuntu VM in Azure within a single evening of hacking. Docker and the docker-compose tool made the deployment and update process extremely quick.
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### Remember linking?
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If you've already been through the [Hands-On Docker tutorial][1] then you will have experience linking Docker containers on the command line. Linking a Node hit counter to a Redis server on the command line may look like this:
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```
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$ docker run -d -P --name redis1
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$ docker run -d hit_counter -p 3000:3000 --link redis1:redis
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```
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Now imagine your application has three tiers
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- Web front-end
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- Batch tier for processing long running tasks
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- Redis or mongo database
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Explicit linking through `--link` is just about manageable with a couple of containers, but can get out of hand as we add more tiers or containers to the application.
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### Enter docker-compose
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>Docker Compose logo
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The docker-compose tool is part of the standard Docker Toolbox and can also be downloaded separately. It provides a rich set of features to configure all of an application's parts through a plain-text YAML file.
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The above example would look like this:
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```
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version: "2.0"
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services:
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redis1:
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image: redis
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hit_counter:
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build: ./hit_counter
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ports:
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- 3000:3000
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```
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From Docker 1.10 onwards we can take advantage of network overlays to help us scale out across multiple hosts. Prior to this linking only worked across a single host. The `docker-compose scale` command can be used to bring on more computing power as the need arises.
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>View the [docker-compose][2] reference on docker.com
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### Real-world example: Raspberry PI Stock Alert
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>The new Raspberry PI Zero v1.3 image courtesy of Pimoroni
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There is a huge buzz around the Raspberry PI Zero - a tiny microcomputer with a 1GHz CPU and 512MB RAM capable of running full Linux, Docker, Node.js, Ruby and many other popular open-source tools. One of the best things about the PI Zero is that costs only 5 USD. That also means that stock gets snapped up really quickly.
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*If you want to try Docker or Swarm on the PI check out the tutorial below.*
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>[Docker Swarm on the PI Zero][3]
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### Original site: whereismypizero.com
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I found a webpage which used screen scraping to find whether 4-5 of the most popular outlets had stock.
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- The site contained a static HTML page
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- Issued one XMLHttpRequest per outlet accessing /public/api/
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- The server issued the HTTP request to each shop and performed the scraping
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Every call to /public/api/ took 3 seconds to execute and using Apache Bench (ab) I was only able to get through 0.25 requests per second.
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### Reinventing the wheel
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The retailers didn't seem to mind whereismypizero.com scraping their sites for stock, so I set about writing a similar tool from the ground up. I had the intention of handing a much higher amount of requests per second through caching and de-coupling the scrape from the web tier. Redis was the perfect tool for the job. It allowed me to set an automatically expiring key/value pair (i.e. a simple cache) and also to transmit messages between Node processes through pub/sub.
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>Fork or star the code on Github: [alexellis/pi_zero_stock][4]
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If you've worked with Node.js before then you will know it is single-threaded and that any CPU intensive tasks such as parsing HTML or JSON could lead to a slow-down. One way to mitigate that is to use a second worker process and a Redis messaging channel as connective tissue between this and the web tier.
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- Web tier
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-Gives 200 for cache hit (Redis key exists for store)
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-Gives 202 for cache miss (Redis key doesn't exist, so issues message)
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-Since we are only ever reading a Redis key the response time is very quick.
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- Stock Fetcher
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-Performs HTTP request
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-Scrapes for different types of web stores
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-Updates a Redis key with a cache expire of 60 seconds
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-Also locks a Redis key to prevent too many in-flight HTTP requests to the web stores.
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```
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version: "2.0"
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services:
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web:
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build: ./web/
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ports:
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- "3000:3000"
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stock_fetch:
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build: ./stock_fetch/
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redis:
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image: redis
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```
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*The docker-compose.yml file from the example.*
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Once I had this working locally deploying to an Ubuntu 16.04 image in the cloud (Azure) took less than 5 minutes. I logged in, cloned the repository and typed in `docker compose up -d`. That was all it took - rapid prototyping a whole system doesn't get much better. Anyone (including the owner of whereismypizero.com) can deploy the new solution with just two lines:
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```
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$ git clone https://github.com/alexellis/pi_zero_stock
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$ docker-compose up -d
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```
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Updating the site is easy and just involves a `git pull` followed by a `docker-compose up -d` with the `--build` argument passed along.
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If you are still linking your Docker containers manually, try Docker Compose for yourself or my code below:
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>Fork or star the code on Github: [alexellis/pi_zero_stock][5]
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### Check out the test site
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The test site is currently deployed now using docker-compose.
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>[stockalert.alexellis.io][6]
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Preview as of 16th of May 2016
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----------
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via: http://blog.alexellis.io/rapid-prototype-docker-compose/
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作者：[Alex Ellis][a]
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译者：[译者ID](https://github.com/译者ID)
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校对：[校对者ID](https://github.com/校对者ID)
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本文由 [LCTT](https://github.com/LCTT/TranslateProject) 原创翻译，[Linux中国](https://linux.cn/) 荣誉推出
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[a]: http://blog.alexellis.io/author/alex/
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[1]: http://blog.alexellis.io/handsondocker
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[2]: https://docs.docker.com/compose/compose-file/
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[3]: http://blog.alexellis.io/dockerswarm-pizero/
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[4]: https://github.com/alexellis/pi_zero_stock
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[5]: https://github.com/alexellis/pi_zero_stock
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[6]: http://stockalert.alexellis.io/
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@ -0,0 +1,142 @@
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通过docker-compose进行快速原型设计
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========================================
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在这篇文章中，我们将考察一个Node.js原型，该原型用于从英国三个主要折扣网店查找“Raspberry PI Zero”的库存。
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我写好了代码，然后经过一晚的hacking把它部署在Aure上的Ubuntu虚拟机上。Docker和docker-compose工具使得部署和更新过程非常快。
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### 还记得链接指令吗？
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如果你已经阅读过[Hands-on Docker tutorial][1]，那么你应该已经可以使用命令行链接Docker容器。通过命令行将节点命中计数器链接到Redis服务器，其命令可能如下所示：
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```
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$ docker run -d -P --name redis1
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$ docker run -d hit_counter -p 3000:3000 --link redis1:redis
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```
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现在假设你的应用程序分为三层：
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- Web前端
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- 处理长时间运行任务的批处理层
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- Redis或者mongo数据库
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通过`--link`的显式链接只是可以用几个容器来管理，但是可能会因为我们向应用程序添加更多层或容器而失控。
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###加入docker-compose
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>Docker Compose logo
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docker-compose工具是标准Docker工具箱的一部分，也可以单独下载。 它提供了一组丰富的功能，通过纯文本YAML文件配置所有应用程序的部件。
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上面的例子看起来像这样：
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```
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version: "2.0"
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services:
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redis1:
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redis1:
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image: redis
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hit_counter:
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build: ./hit_counter
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ports:
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- 3000:3000
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```
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从Docker 1.10开始，我们可以利用网络覆盖来帮助我们在多个主机上进行扩展。 在此之前，链接仅在单个主机上工作。 “docker-compose scale”命令可以用来在需要时带来更多的计算能力。
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>查看docker.com上的[docker-compose] [2]参考
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真实工作示例：Raspberry PI股票警示
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>新的Raspberry PI Zero v1.3图片由Pimoroni提供
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Raspberry PI Zero嗡嗡作响 - 它是一个极小的微型计算机，具有1GHz CPU和512MB RAM，可以运行完整的Linux、Docker、Node.js、Ruby和其他许多流行的开源工具。 PI Zero最好的优点之一就是它成本只有5美元。 这也意味着它去库存的速度非常之快。
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*如果你想在PI上尝试Docker和Swarm，请查看下面的教程。*
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>[Docker Swarm on the PI Zero][3]
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### 原始网站：whereismypizero.com
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我发现一个网页，它使用屏幕抓取以找出4-5个最受欢迎的折扣网店是否有库存。
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- 网站包含静态HTML网页
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- 向每个折扣网店发出一个XMLHttpRequest访问/ public / api /
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- 服务器向每个网店发出HTTP请求并执行抓屏
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每一次对/ public / api /的调用，其执行花3秒钟，而使用Apache Bench（ab），我每秒只能得到0.25个请求。
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### 重新发明轮子
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零售商似乎并不介意whereismypizero.com抓取他们的网站的商品库存信息，所以我开始从头写一个类似的工具。 我有意通过缓存和解耦从web层处理更多的抓取请求。 Redis是执行这项工作的完美工具。 它允许我设置一个自动过期的键/值对（即一个简单的缓存），还可以通过pub / sub在节点进程之间传输消息。
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>复刻或者追踪github上的代码: [alexellis/pi_zero_stock][4]
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如果之前使用过Node.js，你肯定知道它是单线程的，并且任何CPU密集型任务，如解析HTML或JSON都可能导致速度放缓。 一种缓解这种情况的方法是使用一个工作进程和Redis消息通道作为它和web层之间的连接组织。
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- Web层
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使用200作为缓冲命中（存储Redis键）
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使用202作为高速缓存未命中（Redis键不存在，因此出现问题消息）
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因为我们只是读一个Redis键，响应时间非常快。
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- 库存抓取器
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执行HTTP请求
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用于在不同类型的网店上抓屏
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更新具有高速缓存超时时间为60秒的Redis键
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另外，锁定一个Redis键，以防止过多的HTTP请求到网店。
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```
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version: "2.0"
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services:
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web:
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build: ./web/
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ports:
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- "3000:3000"
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stock_fetch:
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build: ./stock_fetch/
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redis:
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image: redis
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```
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*来自示例的docker-compose.yml文件*
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一旦本地正常工作，再向Azure的Ubuntu 16.04镜像云部署就轻车熟路，只花了不到5分钟。 我登录，克隆仓库并键入“docker compose up -d”， 这就是所有的工作 - 快速实现整个系统的原型不会比这几个步骤更多。 任何人（包括whereismypizero.com的所有者）只需两行命令就可以部署新解决方案：
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```
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$ git clone https://github.com/alexellis/pi_zero_stock
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$ docker-compose up -d
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```
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更新网站很容易，只需要一个`git pull'`命令，然后执行`docker-compose up -d`命令，该命令需要带上`--build`参数。
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如果你仍然手动链接你的Docker容器，请自己或使用如下我的代码尝试Docker Compose：
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>复刻或者追踪github上的代码： [alexellis/pi_zero_stock][5]
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###一睹测试网站芳容
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目前测试网站使用docker-compose部署。
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>[stockalert.alexellis.io][6]
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预览截止2016年5月16日
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----------
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via: http://blog.alexellis.io/rapid-prototype-docker-compose/
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作者：[Alex Ellis][a]
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译者：[firstadream](https://github.com/firstadream)
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校对：[校对者ID](https://github.com/校对者ID)
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本文由 [LCTT](https://github.com/LCTT/TranslateProject) 原创翻译，[Linux中国](https://linux.cn/) 荣誉推出
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[a]: http://blog.alexellis.io/author/alex/
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[1]: http://blog.alexellis.io/handsondocker
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[2]: https://docs.docker.com/compose/compose-file/
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[3]: http://blog.alexellis.io/dockerswarm-pizero/
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[4]: https://github.com/alexellis/pi_zero_stock
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[5]: https://github.com/alexellis/pi_zero_stock
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[6]: http://stockalert.alexellis.io/
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