Getting 503 Server unavailable while running the perf benchmark python scripts post configuring ca certs

I am trying to do the performance benchmark testing for istio with custom certificates.

as per Istioldie 1.7 / Plugging in existing CA Certificates , have configured the sample certs available with istio downloads. and post that if I run the python script as mentioned tools/perf/benchmark at master · istio/tools · GitHub getting 503 error. below is the actual response while running the python script. can someone let me know what could have been missed in the configurations.

“kubectl --namespace twopods-istio exec fortioclient-5766c94646-b62bv – fortio load -jitter=True -c 2 -qps 1000 -t 100s -a -r 0.001 -httpbufferkb=128 -labels b196104b_qps_1000_c_2_1024_v2-stats-nullvm_both -----------------------
Defaulting container name to captured.
Use ‘kubectl describe pod/fortioclient-5766c94646-b62bv -n twopods-istio’ to see all of the containers in this pod.
Fortio 1.11.3 running at 1000 queries per second, 64->64 procs, for 1m40s: http://fortioserver:8080/echo?size=1024
12:02:11 I httprunner.go:82> Starting http test for --------------------- with 2 threads at 1000.0 qps
12:02:11 W http_client.go:693> Parsed non ok code 503 (HTTP/1.1 503)
Aborting because of error 503 for http://fortioserver:8080/echo?size=1024: “HTTP/1.1 503 Service Unavailable\r\ndate: Tue, 22 Dec 2020 12:02:11 GMT\r\nserver: envoy\r\ncontent-length: 0\r\nx-envoy-upstream-service-time: 64\r\n\r\n”
command terminated with exit code 1”

Thank you