standalone_crawly.md

Running Crawly as a standalone application

An approach that involves abstracting all scraping tasks into a separate entity (or service), thereby allowing you to extract your desired data without the need for Crawly in your mix file.

In other words:

Run Crawly as a Docker container with spiders mounted from the outside.

Getting started

Here we will show how re-implement the example from Quickstart, to achieve the same results with a standalone version of Crawly.

1. Make a folder for your project: mkdir myproject

2. Make spiders folder inside the project folder: mkdir ./myproject/spiders

3. Copy the spider code inside a file in a folder defined on the previous step myproject/spiders/books_to_scrape.ex:

   defmodule BooksToScrape do
       use Crawly.Spider
       @impl Crawly.Spider
       def base_url(), do: "https://books.toscrape.com/"
       @impl Crawly.Spider
       def init() do
           [start_urls: ["https://books.toscrape.com/"]]
       end
       @impl Crawly.Spider
       def parse_item(response) do
           # Parse response body to document
           {:ok, document} = Floki.parse_document(response.body)
           # Create item (for pages where items exists)
           items =
           document
           |> Floki.find(".product_pod")
           |> Enum.map(fn x ->
               %{
               title: Floki.find(x, "h3 a") |> Floki.attribute("title") |> Floki.text(),
               price: Floki.find(x, ".product_price .price_color") |> Floki.text(),
               url: response.request_url
               }
           end)
           next_requests =
           document
           |> Floki.find(".next a")
           |> Floki.attribute("href")
           |> Enum.map(fn url ->
               Crawly.Utils.build_absolute_url(url, response.request.url)
               |> Crawly.Utils.request_from_url()
           end)
           %{items: items, requests: next_requests}
       end
   end

   3. Now create a configuration file using erlang.config format: https://www.erlang.org/doc/man/config.html

      For example: myproject/crawly.config

      [{crawly, [
          {closespider_itemcount, 500},
          {closespider_timeout, 20},
          {concurrent_requests_per_domain, 2},
      
          {middlewares, [
              'Elixir.Crawly.Middlewares.DomainFilter',
              'Elixir.Crawly.Middlewares.UniqueRequest',
              'Elixir.Crawly.Middlewares.RobotsTxt',
              {'Elixir.Crawly.Middlewares.UserAgent', [
                  {user_agents, [<<"Crawly BOT">>]}
              ]}
          ]},
      
          {pipelines, [
              {'Elixir.Crawly.Pipelines.Validate', [{fields, [title, url]}]},
              {'Elixir.Crawly.Pipelines.DuplicatesFilter', [{item_id, title}]},
              {'Elixir.Crawly.Pipelines.JSONEncoder'},
              {'Elixir.Crawly.Pipelines.WriteToFile', [{folder, <<"/tmp">>}, {extension, <<"jl">>}]}
              ]
          }]
      }].

   4. Now lets start the Crawly (First pull it from DockerHub: docker pull oltarasenko/crawly:0.15.0):

      docker run --name crawly -e "SPIDERS_DIR=/app/spiders" \
       -it -p 4001:4001 -v $(pwd)/spiders:/app/spiders \
       -v $(pwd)/crawly.config:/app/config/crawly.config \
       crawly
      

      You can either fetch the latest version of Crawly from DockerHub or built it yourself (docker build -t crawly .)

      ** SPIDERS_DIR environment variable specifies a folder from which additional spiders are going to be fetched. ./spiders is used by default

   5. Open Crawly Web Management interface in your browser: https://localhost:4001/

   Here it's possible to Schedule a spider with a use of Schedule button. The interface also allows you to access other useful information like:

   1. History of your jobs
   2. Items
   3. Logs of the given spider