have a look on this https://istio.io/docs/ops/common-problems/network-issues/#503-errors-after-setting-destination-rule
& i also find this issue on github Authorization Policy issue with 503 check it may be this will solve your problem
have a look on this https://istio.io/docs/ops/common-problems/network-issues/#503-errors-after-setting-destination-rule
& i also find this issue on github Authorization Policy issue with 503 check it may be this will solve your problem