Generate K8s OpenAPI v3 Spec Using from a K8s API Server

k8s-openapi.sh

#!/usr/bin/env bash
# ---
# k8s-openapi.sh
#
# Generate openapi v3 spec from a k8s apiserver and launch a swagger UI
# instance to check it out.
#
# Assumes that k8s api server has been proxied on localhost:8001
# (ie be sure to run `kubectl proxy` prior to execution).
#
# The OpenAPI v3 spec is split out by api group on the k8s api server.
# All the different api groups and their OpenAPI v3 spec urls are
# located at /openapi/v3. This script takes all the spec urls listed
# from /openapi/v3, downloads them, and merges them together into
# a singular spec document that can be read by the swagger ui.
#
# More information on k8s OpenAPI v3 support:
# https://kubernetes.io/docs/concepts/overview/kubernetes-api/#openapi-v3
#
# Process for OpenAPI v2 can be found here:
# https://jonnylangefeld.com/blog/kubernetes-how-to-view-swagger-ui
# 
# jq cheatsheet: https://lzone.de/cheat-sheet/jq
#
# jq map merge magic: https://gist.github.com/crazed/b5448baeb204eb816eb9
#
# Bash multi-line variable magic:
# https://unix.stackexchange.com/questions/275794/iterating-over-multiple-line-string-stored-in-variable
# ---
#
# --- BEGIN LICENSE ---
# Copyright 2023 Ryan Drew
#
# Permission is hereby granted, free of charge, to any person obtaining 
# a copy of this software and associated documentation files (the "Software"),
# to deal in the Software without restriction, including without limitation the
# rights to use, copy, modify, merge, publish, distribute, sublicense, and/or
# sell copies of the Software, and to permit persons to whom the Software is
# furnished to do so, subject to the following conditions:
#
# The above copyright notice and this permission notice shall be included in
# all copies or substantial portions of the Software.
#
# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
# AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
# OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
# THE SOFTWARE.
# --- END LICENSE ---
set -e

mkdir -p /tmp/k8s-openapi
pushd /tmp/k8s-openapi

curl localhost:8001/openapi/v3 > ./paths.json

paths="$(cat ./paths.json | \
jq -r '.paths | to_entries[] | [.key, .value.serverRelativeURL] | join(" ")')"

while IFS= read -r line
do
    name=$(echo $line | cut -d ' ' -f 1)
    url=$(echo $line | cut -d ' ' -f 2)
    echo $name
    curl localhost:8001$url > $(echo $name | tr / _).openapi.json
done <<< $paths

jq -r -s 'reduce .[] as $x ({}; . * $x)' *.openapi.json > ./k8s-openapi-spec.json

docker run --rm -it \
    -v /tmp/k8s-openapi/k8s-openapi-spec.json:/k8s-openapi-spec.json:Z \
    -e SWAGGER_JSON=/k8s-openapi-spec.json \
    -p 8080:8080 \
    swaggerapi/swagger-ui