Implementing a RESTful API with Ruby

APIs are often one the most powerful vectors for driving product adoption, but are often times bolted onto a SaaS offering as an after-thought. There are many different interpretations (some much looser than others) of what makes an API “RESTful”. At Librato we practice “API-first” development where our API’s are specified, tested, implemented, and finally used to add new features to our own products prior to providing them to our users.

1. Implementing a RESTful API w/Ruby “The Right Way” Wednesday, September 21, 2011
2. metrics.librato.com Increase service flexibility/utility Free users’ data Build business value Why APIs? Wednesday, September 21, 2011
3. metrics.librato.com Consumes arbitrary time series data Store it, visualize it, analyze it Query it back out from API Rich client interface Librato Metrics Wednesday, September 21, 2011
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5. metrics.librato.com Requirements Easy to implement and maintain Performant and scalable Easy to understand and use Wednesday, September 21, 2011
6. metrics.librato.com What is REST? Wednesday, September 21, 2011
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8. metrics.librato.com L2 - CRUD URIs HTTP Methods Wednesday, September 21, 2011
9. metrics.librato.com L3 - REST REpresentational State Transfer HATEOAS Hypermedia Constraint Wednesday, September 21, 2011
10. metrics.librato.com “[hypertext constraint is] most often violated within so-called REST APIs ... adhere to them or choose some other buzzword for your API.” - Roy Fielding Wednesday, September 21, 2011
11. metrics.librato.com CRUD API Resources identified/addressed by URI URI Templates HTTP-based interactions Wednesday, September 21, 2011
12. metrics.librato.com Resources Anything we expose to the Web Resources have representations JSON,XML,PNG Services exchange representations Wednesday, September 21, 2011
13. metrics.librato.com URIs Uniform Resource Identifier Uniquely identifies a web resource Makes it addressable http://example.org/resource/123 Wednesday, September 21, 2011
14. metrics.librato.com API Design Constraints JSON output JSON and x-form-urlencoded input Basic HTTP Authentication over SSL Wednesday, September 21, 2011
15. metrics.librato.com Doc. Driven Design URI template Markdown file per-resource URI, parameters, examples Production ready before a single LOC! Wednesday, September 21, 2011
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17. metrics.librato.com Test Driven Dev. Simulate requests against the API Assert expectations about the response test-unit + rack-test Wednesday, September 21, 2011
18. metrics.librato.com Test Driven Dev. def test_create_gauge params = {} params[:name] = "my_gauge" post "/gauges", params assert_equal 201, last_response.status assert last_response.original_headers["Location"] =~ /^\/v1\/gauges\/#{params[:name]}$/ end Wednesday, September 21, 2011
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20. metrics.librato.com Create Resource POST /resource Location: <URI> 201 - Created def test_create create_resource( :name => "some_gauge", :period => 60 ) create_resource( :code => 400, :name => "a" * 256 ) end Wednesday, September 21, 2011
21. metrics.librato.com Read Resource GET /resource/:id 200 OK def test_read name = "my_gauge" gauge = read_resource(:id => name) assert_equal(name, gauge['name']) end Wednesday, September 21, 2011
22. metrics.librato.com Update Resource PUT /resource/:id 204 - No Content def test_update name = "my_gauge" update_resource(:name => name, :period => 300) end Wednesday, September 21, 2011
23. metrics.librato.com Delete Resource DELETE /resource/:id 204 No Content def test_delete name = "my_gauge" delete_resource(:id => name) read_resource(:code => 404, :id => name) end Wednesday, September 21, 2011
24. metrics.librato.com Implementation Wednesday, September 21, 2011
25. metrics.librato.com Implementation CRUD API is a thin layer over your models Sinatra + Sequel Resource per file to_hash method per-model Wednesday, September 21, 2011
26. metrics.librato.com Implementation # CREATE post "/gauges" do unless params[:name] abort_params({:name => ["Must specify gauge name"]}) end if find_gauge(params[:name]) abort_unique({:name => ["Gauge name must be unique"]}) end gauge = create_gauge() halt_created("/gauges/#{gauge.name}") end Wednesday, September 21, 2011
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28. metrics.librato.com Pagination Request offset - starting index into found length - # of resources requested orderby - attribute to sort on sort - ASC/DESC Wednesday, September 21, 2011
29. metrics.librato.com Pagination Response total - # of resources found - # of resources that match the query offset - starting index into found length - # of resources in response Wednesday, September 21, 2011
30. metrics.librato.com Authentication Secure access through SSL/TLS Block port 80 if possible 403 all HTTP requests otherwise Basic Authentication Wednesday, September 21, 2011
31. metrics.librato.com API Versioning URI templates are static Prefer to maintain compatibility Failing that prefer to version your entire API URI? Media Type? Custom Header? Wednesday, September 21, 2011
32. metrics.librato.com URI http://v1.example.org/resource/123 http://example.org/v1/resource/123 http://example.org/resource/123 ?v=1 Wednesday, September 21, 2011
33. metrics.librato.com Media Type Negotiate through Accept header application/json;version=1 Wednesday, September 21, 2011
34. metrics.librato.com Custom HTTP Header X-Api-Version: 1 May not work with legacy clients Don’t do this! Wednesday, September 21, 2011
35. metrics.librato.com Partial Updates PATCH - RFC5789 PATCH /resource/:id Wednesday, September 21, 2011
36. metrics.librato.com HATEOAS CRUD is great except when it isn’t Hypermedia models state transitions Inclusion of links in representation Wednesday, September 21, 2011
37. metrics.librato.com Hypermedia Formats XHTML, ATOM, RSS Domain-specific formats! Add link elements to CRUD format Wednesday, September 21, 2011
38. metrics.librato.com CRUD Pagination { "query":{ "total":128, "found":128, "offset":0, "length":100 }, "gauges":[ { "name":"gauge1" }, { "name":"gauge2" }, ... ] } Wednesday, September 21, 2011
39. metrics.librato.com REST Pagination { "next":{ "uri":"http://api.librato.com/gauges?offset=100”, "rel":"http://relations.librato.com/paginate", "media_type":"application/vnd.librato+json" }, "gauges":[ { "name":"gauge1" }, { "name":"gauge2" }, ... ] } Wednesday, September 21, 2011
40. metrics.librato.com Link Elements uri attribute describes resource rel attribute contains semantic markup link elements can be added/removed from representations Wednesday, September 21, 2011
41. metrics.librato.com GLory of REST Single bookmarked URI Next states are discovered inline Series of representation exchanges transforms application state Wednesday, September 21, 2011
42. metrics.librato.com Have an API and build it first At least use CRUD Docs -> Tests -> Code Make it DRY Dogfood It Learn more about REST Wednesday, September 21, 2011
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46. metrics.librato.com “be conservative in what you do, be liberal in what you accept from others” - Postel’s Law Wednesday, September 21, 2011
47. metrics.librato.com Q&A Wednesday, September 21, 2011