Kubernetes nginx-ingress rewriting for SPA

ingress.yaml

# The rewrite rule for nginx is to pick the first capture group’s match $1 from the path matcher.
#
# In the path matcher regex there are 2 capture groups (the inner groups are not captured):
# /(...)|(.*)
#  ^$1   ^$2
#
# So when we match anything that starts with "/api/" or ends with one of "css"/"js"/"png" this will
# populate $1 and nginx passes the url unaltered upstream (-> /$1). If there is no such match, we match
# everything else through the alternation: (.*) to populate $2, but we throw $2 away (we don't make use
# of it in the rewrite target! An empty capture group, in this second scenario $1, will turn into an
# empty string in the rewrite expression, thus "/$1" becomes "/", which is going to load the SPA in
# this case. In the browser the url won’t change and the client-side router takes over.
apiVersion: networking.k8s.io/v1
kind: Ingress
metadata:
  name: ingress
  annotations:
    nginx.ingress.kubernetes.io/rewrite-target: /$1
spec:
  ingressClassName: nginx
  rules:
    - host: example.com
      http:
        paths:
          - path: "/((?:api/.*|.*(?:css|js|png)$))|(.*)"
            pathType: Prefix
            backend:
              service:
                name: service
                port:
                  number: 8888