From REST to gRPC: An API Evolution Story Joe Runde Michael Keeling IBM IBM @joerunde @michaelkeeling 2 What is gRPC? Open source Remote Procedure Call framework 3 What is gRPC? Open source Remote Procedure Call framework “… a modern, bandwidth and CPU efficient, low latency way to create massively distributed systems that span data centers” 4 Why should we use gRPC? 5 Why is gRPC awesome? Performance 6 Performance Benefits HTTP / REST 7 Performance Benefits HTTP / REST gRPC 8 How does gRPC improve performance? • HTTP/2 transport protocol • Binary encodings via protocol buffers • No more parsing text! • Compression • Streaming 9 Why is gRPC awesome? Performance 10 Why is gRPC awesome? Performance Remote Procedure Calls 11 REST setup is tedious headers = {} headers.put(“X-FooBar-User”, user.getFooBarID()) headers.put(“FooBarTransaction”, app.getNextTxnIDAtomic()) headers.put(“FooBarAlgoType”, ApproximateFoo.toHeaderString()) 12 REST setup is tedious Public class Foo { @JsonProperty(name=”foo_id”) String id; @JsonProperty(name=”bar”) int bar; ... } 13 REST setup is tedious Public class Foo { ... public Foo(@JsonProperty(“foo_id”,required=true) String id, @JsonProperty(“bar”,required=true) int bar) { ... } } 14 RPC setup is easy request = FooService.RequestBuilder() .setId(foo.getId()) .setBar(foo.getBar())... .build(); response = fooClient.DoFooBar(request); 15 Why is gRPC Awesome? Performance Remote Procedure Calls 16 Why is gRPC Awesome? Performance Remote Procedure Calls Strategic Direction of our Platform 17 18 <insert slick demo here> 19 Just one problem… Our current microservices all use REST. 20 21 Business Constraints 22 The Transition Plan • Phase 1: Design gRPC API • Phase 2: Run REST and gRPC services • Phase 3: Transition functional tests • Phase 4: Remove REST functionality 23 DESIGN THE API Phase I 24 Designing a gRPC API REST: gRPC: POST rpc AddFoo(Foo) /api/foo returns FooID; GET rpc GetFoo(FooID) /api/foo/{foo_id} returns Foo; 25 Designing a gRPC API REST: gRPC: POST message Foo { /api/foo FooID id = 1; repeated Bar bars = 2; GET } /api/foo/{foo_id} message FooID { string val = 1; } 26 Designing a gRPC API REST: gRPC: POST rpc AddBar(Bar) /api/foo/{foo_id}/bar returns BarID; GET rpc GetFoo(BarID) /api/foo/{foo_id}/bar/ returns Bar; {bar_id} 27 Designing a gRPC API REST: gRPC: POST rpc AddBar(Bar) /api/foo/{foo_id}/bar returns BarID; GET rpc GetFoo(BarID) /api/foo/{foo_id}/bar/ returns Bar; {bar_id} 28 Designing a gRPC API REST: gRPC: message Bar{ POST BarID id = 1; /api/foo/{foo_id}/bar int baz = 2; } GET /api/foo/{foo_id}/bar/ message BarID { {bar_id} FooID foo_id = 1; string bar_id = 2; } 29 Designing a gRPC API Bar service: /api/foo/{foo_id}/bar/{bar_id} Buzz service: /api/foo/{foo_id}/buzz/{buzz_id} 30 SERVE REST AND GRPC Phase II 31 Current: REST Only REST Caller FooBar Service 32 Future: REST and gRPC REST gRPC Caller Caller FooBar Service 33 We need to evolve our API without damaging basic functionality. 34 Current: Layers View Rest Service Code Package Business Logic Models is allowed to use Datastore Access 35 Future: Layers View Rest gRPC Service Service Code Package Business Logic Models is allowed to use Datastore Access 36 Layer Pattern Rocks! A code review comment: "What's with the service layer? This just passes its inputs to our business logic functions, it's redundant cruft!" 37 Evolving the code went really well… 38 39 Things that suddenly became a problem • Health Checks • API Discovery • No curl • Headers? • SSL? • Simple community examples 40 TRANSITION FUNCTIONAL TESTS Phase III 41 Specification by Example 42 Specification by Example- REST 43 Ruby metaprogramming Choice of programming language really paid off request = Object::const_get( ”FooBar::#{message_name}").decode_json(json) response = client.method(method_name.to_sym) .call(request) 44 Specification by Example- gRPC 45 200+ tests transitioned in 1 week 46 Why did this go so well? • Expressiveness of spec by example • Flexibility of Ruby • gRPC can decode JSON 47 REMOVE REST FUNCTIONALITY Phase IV 48 rm –rf src/*rest* 49 We need to retain some REST endpoints REST gRPC Caller Caller FooBar Service 50 51 Current Layered Architecture Service Rest gRPC Service Service FooBar Business Logic Models Service Datastore Access 52 Layers Forked – Two Services REST Service FooBar gRPC Clients Proxy Service gRPC Service FooBar Business Logic Models Service Datastore Access 53 Evil wizards strike again! 54 NOW WE’RE READY FOR RELEASE…? 55 New problems we created • Health Checks • API Discovery • No curl • Headers? • SSL? 56 New problems we created • Health Checks • API Discovery • No curl • Headers? • SSL? 57 API Discovery • REST – Ask the service! • gRPC – Find the (correct) proto file? 58 API Discovery • REST – Ask the service! • gRPC – Find the (correct) proto file? • Standard InfoService serves github url + version • Snapshot proto files with releases • Client vendors the proto files they use 59 60 Tools support • Basically Nonexistent • Our solutions: • Hand roll mocks for testing • Write new functional tests each time we wanted to use curl 61 Adios, REST! 62 INTERESTING THINGS WE LEARNED 63 • The right kinds of abstractions promote extensibility • Focus on the domain model • Create a specification by example • Take care when choosing frameworks • Deal with risks of technology adoption 64 Would we do it again? 65 Would we do it again? Yes. • Super easy to integrate with a service • Promotes small polyglot services • Difficult to do bad things • Performance is 66 Thank you! Michael Keeling Joe Runde @michaelkeeling @joerunde neverletdown.net Buy Design It! now at http://bit.ly/2pJOrly BACKUP 68 69 70 71 72.