https://kubernetes.github.io/ingress-nginx/user-guide/nginx-configuration/configmap/#log-format-upstream

kubectl apply -f - <<EOF
apiVersion: v1
data:
  log-format-upstream: '{"time": "$time_iso8601","remote_addr": "$remote_addr","x-forward-for":
    "$proxy_add_x_forwarded_for","request_id": "$req_id","remote_user": "$remote_user","bytes_sent":
    "$bytes_sent","request_time": "$request_time","status": "$status","vhost": "$host","request_proto":
    "$server_protocol","path": "$uri","request_query": "$args","request_length": "$request_length","duration":
    "$request_time","method": "$request_method","http_referrer": "$http_referer","http_user_agent":
    "$http_user_agent"}'
kind: ConfigMap
metadata:
  labels:
    app: ingress-nginx
  name: nginx-configuration
  namespace: ingress-nginx
EOF