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Practical guide to building public APIs

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Lessons gained from building HMRCs API platform. A practical guide for those looking to embark upon their own platform.

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Practical guide to building public APIs

  1. 1. simple software solutions to big business problems Making Software. Better. Digital By Default Building APIs for Government
  2. 2. 2 I believe the creation of the Government Digital Service is one of the great unsung triumphs of the last Parliament. Prime Minister David Cameron
  3. 3. Govtalk Webservices - now 4
  4. 4. Where we’ll get to
  5. 5. Why an API platform HMRC wants to improve end-user experience, and reduce errors. An API platform allows HMRC to take control of the business logic again, simplifying integration. By doing that, software vendors produce more innovative products or even better free software
  6. 6. API Benefits for others Organisations can benefit from APIs in many other ways too. Business expansion with limited involvement (franchises) and simpler integration with partners and internal software vendors.
  7. 7. 10 Years of AWS - APIs are forever “.......Once customers started building their applications and systems using our APIs, changing those APIs becomes impossible, as we would be impacting our customer’s business operations if we would do so. We knew that designing APIs was a very important task as we’d only have one chance to get it right.” http://www.allthingsdistributed.com/2016/03/10-lessons-from-10-years-of-aws.html
  8. 8. A Practical GuideTo Building APIs at HMRC Digital Practical Guide to Building APIs
  9. 9. Set out your visionSet out your vision
  10. 10. Always start with a vision Your vision must be ambitious, clear, precise. It must set out where you want to get to, not where you are.
  11. 11. 10 Years of AWS - APIs are forever “.......Once customers started building their applications and systems using our APIs, changing those APIs becomes impossible, as we would be impacting our customer’s business operations if we would do so. We knew that designing APIs was a very important task as we’d only have one chance to get it right.” http://www.allthingsdistributed.com/2016/03/10-lessons-from-10-years-of-aws.html
  12. 12. Your organisation is ready The fact that your organisation wants to create an API platform means they are ready to be better. “We are not mature enough” does not hold.
  13. 13. An API Manifesto At HMRC we have documented our vision into an API Manifesto, that is shared with the business, architects and whole delivery team.
  14. 14. Our APIs are beautiful HMRC Digital’s APIs are more than an interface to our code. They are a reflection of our brand, quality and pride. They are the “web front end” to our services. Beauty is the following of standard RESTFul principles, HMRC Digital API standards and consensus.
  15. 15. Our APIs are RESTFul HMRC Digital APIs are RESTFul and therefore display all the characteristics of REST. There is no acknowledgement of multiple levels of REST and terms such as “Pragmatic REST” and “RPC REST” are not valid.
  16. 16. Our APIs reflect domain - not process HMRC Digital’s APIs are focussed on the domain at hand. We do not reflect business processes as these represent internal implementation.
  17. 17. Our APIs must perform HMRC Digital’s APIs must perform. Volumes, Throughput, Consistency, Accuracy, Security, Ease of Integration. Our APIs take advantage of the web infrastructure for scalability and ubiquity. We only get one chance to make a good impression but hundreds of chances to get it wrong.
  18. 18. Our APIs are built for the end consumer HMRC Digital APIs are not built for a specific system or application. They are not built to fulfil a technical problem. They are built with our end consumer in mind and fulfil customer need.
  19. 19. Our Microservices are API First All our microservices on the platform follow the guidelines of APIs, ensuring all of them are publishable even if not intended to be so.
  20. 20. Be RESTFul Our APIs are RESTFul Our APIs are Beautiful Our APIs must perform Be RESTFul Our APIs must be beautiful Our APIs are RESTFul Our APIs must perform
  21. 21. No Hypermedia, No REST “If the engine of application state (and hence the API) is not being driven by hypertext, then it cannot be RESTful and cannot be a REST API. Period.” - Roy Fielding
  22. 22. Richardsons Maturity Model Courtesy of www. martinfowler.com
  23. 23. But it’s misused and abused Richardson’s Maturity Model has become a justification to not use Hypermedia. It is not meant to be a model for levels of valid REST development. Just an observation of an organisation’s proximity to REST
  24. 24. Examples
  25. 25. Media Types Media types give a structure for the content of your APIs, allowing clients to negotiate through Hypermedia controls without needing prior knowledge of those controls.
  26. 26. Standards Based A number of media types are attempting to be standards is this area. HAL, JSON-LD, Collections+JSON are some of the better known ones in the JSON arena. These tend to be generic and ensure looser coupling.
  27. 27. Examples
  28. 28. Vendor Specific Media Types Vendor specific media types are custom types created for your organisation. These could be general organisation or specific by resource.
  29. 29. Organisation specific While you like the idea of a generic media type for all cases, the standards based ones seem like overkill to you, so one for your entire organisation fits better.
  30. 30. Resource specific Resource specific media types would be created at a resource or domain level. For example, a media type for a customer and one for order etc
  31. 31. Verbs The HTTP spec has 8 standard verbs that the RESTFul Architectural Style takes advantage of. These have their very own characteristics and should be used correctly
  32. 32. GET The GET verb is safe and idempotent according to the spec. Do not abuse this. Clients expect that and if abused can bring about many side effects. Only use to retrieve a resource.
  33. 33. POST The POST verb is neither safe nor idempotent. The HTTP spec does not say how this should be use. However, standard practice is when you wish to create a new resource whose ID is unknown.
  34. 34. PUT The PUT verb is unsafe but idempotent. Standard usage is for creating a new resource where you know the ID or where you an updating an existing resource.
  35. 35. DELETE The DELETE verb is unsafe but idempotent. Does what it says on the tin.
  36. 36. OPTIONS Not widely used enough, the OPTIONS verb gives you information regarding an endpoint - what verbs apply, what content type and relevant documentation. Take advantage of it. Your clients will thank you.
  37. 37. Others PATCH is for partial updates. Best to avoid where possible. HEAD, TRACE and CONNECT rarely used or needed in your API platform
  38. 38. Status Codes HTTP Status Codes provide a standard way to tell the client software what is happening. Use them correctly and they save you a lot of time.
  39. 39. Status Codes - some patterns Use 200 - OK when successfully returning a GET Use 201 - Created when successfully creating a resource return resource location in header Use 202 - Accepted when request is valid and can be created return resource location in header
  40. 40. Caching The REST Architectural Style takes advantage of the web architecture to improve scalability. You need to take advantage of it by using the correct HTTP headers.
  41. 41. Caching HTTP Headers Expires and Cache-Control are the two response headers that allow for caching. These set either expiry date or TTL.
  42. 42. RESTFul means loose coupling By controlling flow and business logic within the API, thereby hiding implementation, you ensure loose coupling between the client and the API.
  43. 43. REST means Smaller Payloads Hypermedia can allow for smaller payloads. This reduces latency by having less sent over the wire but also minimising the amount of orchestration on the server.
  44. 44. REST takes advantage of caching The web architecture allows for caching and taking advantage of the GET method gives us efficient responses.
  45. 45. Better/Cheaper Client Software The biggest advantage of the RESTFul Architectural Style is that it minimises the amount of knowledge your clients need to have about your system. Allowing them to integrate quickly and innovate more rapidly.
  46. 46. Reflect Domain Our APIs are Beautiful Our APIs reflect domain - not process Reflect Domain not Processes Our APIs are beautiful Our APIs reflect domain
  47. 47. Why not business processes? Business processes were not created for the digital world. They were created for cryptic commands into mainframe terminals, paper forms and human (intelligent) intervention. Reflect these digitally and you limit APIs
  48. 48. SOA’s biggest failure SOA made the business process the key part of the process. Business Process Models were the central artefacts. This created services that were too cumbersome and too tightly coupled to the non-digital age.
  49. 49. Domain not processes Create APIs that reflect your domain, using Domain Driven Design concepts. You will not limit yourselves to existing processes, you’ll hide the implementation and you’ll use industry language. In so doing, complexity is reduced/isolated/removed.
  50. 50. An Example
  51. 51. The APIs /users/{id} /users/{id}/roles /users/{id}/ratings /users/{id}/friends /roles/{role} /movies/{movie-name} /movies/{movie-name}/ratings /movies/{movie-name}/actors /actors/{actor-id}
  52. 52. cont…..
  53. 53. cont…..
  54. 54. Versioning Strategy Versioning Strategy Our APIs must perform
  55. 55. To version or not to version
  56. 56. Why it’s best not to version Versioning APIs introduces a number of significant complexities that you would need to overcome. How many versions should you support, how do you support them, what counts as a new version, what sort of deprecation strategy, what if you backend systems are not versioned etc…..
  57. 57. Why you shouldn’t need to version Hypermedia controls should mean your clients are so loosely coupled to your APIs that they need not be affected by changes. They would ignore changes until they are ready.
  58. 58. Why you need to think about versioning What if you cannot prevent breaking changes? What if too many clients are hard coding instead of using Hypermedia controls?
  59. 59. Versioning guidelines - Include versions Include a version number in your APIs - ideally in the header as part of the Accept header but at least as part of the url.
  60. 60. Versioning guidelines - Don’t do it Do everything you can to avoid breaking changes and backwards compatibility. Follow RESTFul guidelines and you will find this easy
  61. 61. Versioning guidelines - Deprecate With every new version, deprecate your old version straight away with a maximum support period for bug fixes. New features will not be included in deprecated version
  62. 62. Ensure Security Secure your APIs Our APIs must perform
  63. 63. Web Security Economics “1. Good enough is good enough. 2. Good enough always beats perfect. 3. The really hard part is determining what is good enough” Prof. Ravi Sandhu
  64. 64. Valet Parking Problem One of the biggest and most prominent issues in web security is over privileging users. Like giving your keys to a valet, they can find out where you live, have your house keys and know where you’ll be for next 2 hours.
  65. 65. Switch on TLS Encryption TLS/SSL performance is no longer the issue it once was. Companies such as Netflix have switched on encryption for its video streaming. With the low overhead it would be silly not to.
  66. 66. HTTP Basic Auth The simplest form of API authentication, uses Base64 encoding. Easiest to implement and easiest integrate with. But also easiest to hack. Encoding is not the same as encryption. Only use with TLS
  67. 67. OAuth 2.0 The current defacto standard for API authentication and authorisation. Will only work with TLS. Works by exchanging of encrypted tokens.
  68. 68. OAuth 2.0 The user is granting access to certain privileges for the software. With trusted clients, implicit grant access can be provided.
  69. 69. OAuth 2.0 Tokens are tied to developers - allowing closing down a link with a developer that may have been compromised rather than the whole platform.
  70. 70. These are not enough Beyond your API platform, the rest of your technical platform must be secure and your organisation must be secure. Techniques such as transaction monitoring and fraud detection can be useful.
  71. 71. Ultimately, it’s about quality All the encryption, TLS, auth, firewalls or big burly bouncers will do you no good if your code has bugs and your design is flawed.
  72. 72. Documenting your APIs Our APIs are beautiful Our APIs are RESTFul
  73. 73. Documentation Tools There are a number of REST JSON documentation tools. RAML, Swagger and Hydra. But they each have flaws.
  74. 74. RAML and Swagger RAML and Swagger are more than just documentation tools. They provide define, build, test and documentation frameworks. However, they do not support RESTFul attributes, in particular hypermedia controls
  75. 75. Hydra Less of a fully functioning framework than the other two but does support hypermedia controls…...but only if you use the JSON-LD media type
  76. 76. Proprietary Documentation It’s important to not be tempted to limit your vision to use those great tools. Instead, in this case, a proprietary documentation tool built in- house will be preferable. Make it easy for your developers.
  77. 77. API Management Tools Our APIs must perform
  78. 78. Features API Management tools provide a number of important features: Manage API Accesses Manage Traffic Monitoring Manage Available APIs
  79. 79. Products Leading API Management tools are provided by WSO2, CA Technologies, Mulesoft, Mashery
  80. 80. Don’t be constrained Your API Manager needs to support your vision. Don’t change your vision for the tool. But don’t try doing it yourselves.
  81. 81. Good API Platforms
  82. 82. ● Github.com https://developer.github. com/v3/pulls/ ● Stormpath.com https://docs.stormpath. com/rest/product- guide/latest/reference. html#application ● Paypal.com https://developer.paypal. com/docs/rest/api/ ● Visa https://developer.visa.com Examples
  83. 83. Homework
  84. 84. 1. Rest in Practice - Jim Webber 2. Domain Driven Design - Eric Evans 3. RESTFul Web Services Cookbook - Subbu Allamajru 4. http://martinfowler.com/articles/richardsonMaturityModel.html 5. Maze+XML by Mike Amundson ○ http://amundsen.com/media-types/maze/ 6. Resource-Oriented Architectures: Hypermedia ○ https://www.safaribooksonline.com/library/view/resource-oriented-architectures- hypermedia/9781491924877 7. Government Digital Service - Digital by Default ○ https://www.gov.uk/service-manual/digital-by-default 8. Introduction to Secure Software ○ https://www.safaribooksonline.com/library/view/introduction-to-secure/9781491943595
  85. 85. Thank You Twitter @EqualExperts LinkedIn linkedin.com/company/equal-experts UNITED KINGDOM +44 203 603 7830 helloUK@equalexperts.com Equal Experts UK Ltd 30 Brock Street London NW1 3FG INDIA +91 20 6607 7763 helloIndia@equalexperts.com Equal Experts India Private Ltd Office No. 4-C Cerebrum IT Park No. B3 Kumar City, Kalyani Nagar Pune, 411006 Web www.equalexperts.com CANADA +1 403 775 4861 helloCanada@equalexperts.com Equal Experts Devices Inc 205 - 279 Midpark way S.E. T2X 1M2 Calgary, Alberta Twitter: @softwarereda LinkedIn: linkedin.com/in/redahmeid

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