diff --git a/sources/tech/20160512 Rapid prototyping with docker-compose.md b/sources/tech/20160512 Rapid prototyping with docker-compose.md new file mode 100644 index 0000000000..0c67223697 --- /dev/null +++ b/sources/tech/20160512 Rapid prototyping with docker-compose.md @@ -0,0 +1,142 @@ + +Rapid prototyping with docker-compose +======================================== + +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. + +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. + +### Remember linking? + +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: + +``` +$ docker run -d -P --name redis1 +$ docker run -d hit_counter -p 3000:3000 --link redis1:redis +``` + +Now imagine your application has three tiers + +- Web front-end +- Batch tier for processing long running tasks +- Redis or mongo database + +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. + +### Enter docker-compose + +![](http://blog.alexellis.io/content/images/2016/05/docker-compose-logo-01.png) +>Docker Compose logo + +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. + +The above example would look like this: + +``` +version: "2.0" +services: + redis1: + image: redis + hit_counter: + build: ./hit_counter + ports: + - 3000:3000 +``` + +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. + +>View the [docker-compose][2] reference on docker.com + +### Real-world example: Raspberry PI Stock Alert + +![](http://blog.alexellis.io/content/images/2016/05/Raspberry_Pi_Zero_ver_1-3_1_of_3_large.JPG) +>The new Raspberry PI Zero v1.3 image courtesy of Pimoroni + +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. + +*If you want to try Docker or Swarm on the PI check out the tutorial below.* + +>[Docker Swarm on the PI Zero][3] + +### Original site: whereismypizero.com + +I found a webpage which used screen scraping to find whether 4-5 of the most popular outlets had stock. + +- The site contained a static HTML page +- Issued one XMLHttpRequest per outlet accessing /public/api/ +- The server issued the HTTP request to each shop and performed the scraping + +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. + +### Reinventing the wheel + +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. + +>Fork or star the code on Github: [alexellis/pi_zero_stock][4] + +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. + +- Web tier + -Gives 200 for cache hit (Redis key exists for store) + -Gives 202 for cache miss (Redis key doesn't exist, so issues message) + -Since we are only ever reading a Redis key the response time is very quick. +- Stock Fetcher + -Performs HTTP request + -Scrapes for different types of web stores + -Updates a Redis key with a cache expire of 60 seconds + -Also locks a Redis key to prevent too many in-flight HTTP requests to the web stores. +``` +version: "2.0" +services: + web: + build: ./web/ + ports: + - "3000:3000" + stock_fetch: + build: ./stock_fetch/ + redis: + image: redis +``` + +*The docker-compose.yml file from the example.* + +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: + +``` +$ git clone https://github.com/alexellis/pi_zero_stock +$ docker-compose up -d +``` + +Updating the site is easy and just involves a `git pull` followed by a `docker-compose up -d` with the `--build` argument passed along. + +If you are still linking your Docker containers manually, try Docker Compose for yourself or my code below: + +>Fork or star the code on Github: [alexellis/pi_zero_stock][5] + +### Check out the test site + +The test site is currently deployed now using docker-compose. + +>[stockalert.alexellis.io][6] + +![](http://blog.alexellis.io/content/images/2016/05/Screen-Shot-2016-05-16-at-22-34-26-1.png) + +Preview as of 16th of May 2016 + +---------- +via: http://blog.alexellis.io/rapid-prototype-docker-compose/ + +作者：[Alex Ellis][a] +译者：[译者ID](https://github.com/译者ID) +校对：[校对者ID](https://github.com/校对者ID) + +本文由 [LCTT](https://github.com/LCTT/TranslateProject) 原创翻译，[Linux中国](https://linux.cn/) 荣誉推出 + +[a]: http://blog.alexellis.io/author/alex/ +[1]: http://blog.alexellis.io/handsondocker +[2]: https://docs.docker.com/compose/compose-file/ +[3]: http://blog.alexellis.io/dockerswarm-pizero/ +[4]: https://github.com/alexellis/pi_zero_stock +[5]: https://github.com/alexellis/pi_zero_stock +[6]: http://stockalert.alexellis.io/ +