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143 lines
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143 lines
6.1 KiB
Markdown
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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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