Kubernetes Clients and OpenAPI Generator William Cheng - @wing328 24 Jun, 2019

Kubernetes Clients Official - C#, Go, Java, Python, Javascript (reference) - Maintained by Kubernetes SIG API Machinery Unofficial (community-maintained) - PHP, Lisp, Elixir, Haskel, etc. Ref: https://kubernetes.io/docs/reference/using-api/client-libraries/ Manual vs auto-generated

Official Kubernetes - past, present, future ● Past ○ Go: https://github.com/kubernetes/client-go/ (auto-generated by AutoRest) ○ Python, Java, etc: auto-generated by Swagger Codegen (https://github.com/swagger-api/swagger-codegen) ● Present ○ Switching to OpenAPI Generator (https://github.com/openapitools/openapi-generator) ● Future ○ Support more clients (e.g. Elixir, Rust, etc) ○ Add more tests to ensure the client works as expected ○ Fix issues upstream in Openapi Generator

Why code generation? ● If the REST API is documented in OpenAPI (f.ka. Swagger) spec, one can easily generate clients, server stubs, documentation, etc using generators (openapi-generator, nswag, go-swagger) ● Pros ○ Save time ○ Scalable ○ Consistent developer experience ○ Code maturity ○ Maintainability ● Cons ○ Edge cases ○ Machine-generated code not human friendly

OpenAPI/Swagger Spec 1. Swagger specification donated to Linux Foundation to form OpenAPI Initiative backed by IBM, Google, Microsoft, PayPal, Atlassian etc in 2015 2. Renamed to OpenAPI Specification (OAS) 3. OpenAPI 3.0 officially released in July 2017 - Enhancements: anyOf, oneOf, nullable, etc References: 1. OpenAPI 2.0 spec 2. OpenAPI 3.0 spec

OpenAPI spec examples Petstore (OpenAPI spec 2.0) Petstore (OpenAPI spec 3.0) Kubernetes API (OpenAPI spec 2.0)

OpenAPI Generator ● Generate clients, servers, documentation, schema given an OpenAPI/Swaggers specifications ● A fork of Swagger Codegen (May 2018): Reasons of the fork: Q&A ● Formed by ~50 top contributors/template creators ● Support 100+ generators (newly added: C client generator) ● May 2019: 4.0.0 released (the 21st release) ● Kubernetes client: Migrate from swagger-codegen to openapi-generator

Who’s using OpenAPI Generator?

Example - Kubernetes Perl client 1. Generate Perl client for Kubernetes using OpenAPI (script, config) 2. Perform testings 3. Report bugs to OpenAPI Generator (issue tracker) 4. Get help from the community 5. Fix the issue in OpenAPI Generator (example) 6. Tested the fix (SNAPSHOT version) after the fix (PR) is merged 7. Deploy the stable release of OpenAPI Generator to the workflow

Any questions?