<p>I have a GKE cluster (gke v1.13.6) and using istio (v1.1.7) with several services deployed and working successfully except one of them which always responds with HTTP 503 when calling through the gateway : upstream connect error or disconnect/reset before headers. reset reason: connection failure.</p>

<p>I've tried calling the pod directly from another pod with curl enabled and it ends up in 503 as well :</p>

<pre><code>$ kubectl exec sleep-754684654f-4mccn -c sleep -- curl -v d-vine-machine-dev:8080/d-vine-machine/swagger-ui.html
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
  0     0    0     0    0     0      0      0 --:--:-- --:--:-- --:--:--     0*   Trying 10.3.254.3...
* TCP_NODELAY set
* Connected to d-vine-machine-dev (10.3.254.3) port 8080 (#0)
&gt; GET /d-vine-machine/swagger-ui.html HTTP/1.1
&gt; Host: d-vine-machine-dev:8080
&gt; User-Agent: curl/7.60.0
&gt; Accept: */*
&gt;
upstream connect error or disconnect/reset before headers. reset reason: connection failure&lt; HTTP/1.1 503 Service Unavailable
&lt; content-length: 91
&lt; content-type: text/plain
&lt; date: Thu, 04 Jul 2019 08:13:52 GMT
&lt; server: envoy
&lt; x-envoy-upstream-service-time: 60
&lt;
{ [91 bytes data]
100    91  100    91    0     0   1338      0 --:--:-- --:--:-- --:--:--  1378
* Connection #0 to host d-vine-machine-dev left intact
</code></pre>

<p>Setting the log level to TRACE at the istio-proxy level :</p>

<pre><code>$ kubectl exec -it -c istio-proxy d-vine-machine-dev-b8df755d6-bpjwl -- curl -X POST http://localhost:15000/logging?level=trace
</code></pre>

<p>I looked into the logs of the injected sidecar istio-proxy and found this :</p>

<pre><code>[2019-07-04 07:30:41.353][24][debug][router] [external/envoy/source/common/router/router.cc:381] [C119][S9661729384515860777] router decoding headers:
':authority', 'api-dev.d-vine.tech'
':path', '/d-vine-machine/swagger-ui.html'
':method', 'GET'
':scheme', 'http'
'cache-control', 'max-age=0'
'upgrade-insecure-requests', '1'
'user-agent', 'Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/75.0.3770.100 Safari/537.36'
'accept', 'text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,image/apng,*/*;q=0.8,application/signed-exchange;v=b3'
'accept-encoding', 'gzip, deflate'
'accept-language', 'fr-FR,fr;q=0.9,en-US;q=0.8,en;q=0.7'
'x-forwarded-for', '10.0.0.1'
'x-forwarded-proto', 'http'
'x-request-id', 'e38a257a-1356-4545-984a-109500cb71c4'
'content-length', '0'
'x-envoy-internal', 'true'
'x-forwarded-client-cert', 'By=spiffe://cluster.local/ns/default/sa/default;Hash=8b6afba64efe1035daa23b004cc255e0772a8bd23c8d6ed49ebc8dabde05d8cf;Subject="O=";URI=spiffe://cluster.local/ns/istio-system/sa/istio-ingressgateway-service-account;DNS=istio-ingressgateway.istio-system'
'x-b3-traceid', 'f749afe8b0a76435192332bfe2f769df'
'x-b3-spanid', 'bfc4618c5cda978c'
'x-b3-parentspanid', '192332bfe2f769df'
'x-b3-sampled', '0'

[2019-07-04 07:30:41.353][24][debug][pool] [external/envoy/source/common/http/http1/conn_pool.cc:88] creating a new connection
[2019-07-04 07:30:41.353][24][debug][client] [external/envoy/source/common/http/codec_client.cc:26] [C121] connecting
[2019-07-04 07:30:41.353][24][debug][connection] [external/envoy/source/common/network/connection_impl.cc:644] [C121] connecting to 127.0.0.1:8080
[2019-07-04 07:30:41.353][24][debug][connection] [external/envoy/source/common/network/connection_impl.cc:653] [C121] connection in progress
[2019-07-04 07:30:41.353][24][debug][pool] [external/envoy/source/common/http/conn_pool_base.cc:20] queueing request due to no available connections
[2019-07-04 07:30:41.353][24][trace][http] [external/envoy/source/common/http/conn_manager_impl.cc:811] [C119][S9661729384515860777] decode headers called: filter=0x4f118b0 status=1
[2019-07-04 07:30:41.353][24][trace][http] [external/envoy/source/common/http/http1/codec_impl.cc:384] [C119] parsed 1272 bytes
[2019-07-04 07:30:41.353][24][trace][connection] [external/envoy/source/common/network/connection_impl.cc:282] [C119] readDisable: enabled=true disable=true
[2019-07-04 07:30:41.353][24][trace][connection] [external/envoy/source/common/network/connection_impl.cc:440] [C121] socket event: 3
[2019-07-04 07:30:41.353][24][trace][connection] [external/envoy/source/common/network/connection_impl.cc:508] [C121] write ready
[2019-07-04 07:30:41.353][24][debug][connection] [external/envoy/source/common/network/connection_impl.cc:526] [C121] delayed connection error: 111
[2019-07-04 07:30:41.353][24][debug][connection] [external/envoy/source/common/network/connection_impl.cc:183] [C121] closing socket: 0
[2019-07-04 07:30:41.353][24][debug][client] [external/envoy/source/common/http/codec_client.cc:82] [C121] disconnect. resetting 0 pending requests
[2019-07-04 07:30:41.353][24][debug][pool] [external/envoy/source/common/http/http1/conn_pool.cc:129] [C121] client disconnected, failure reason:
[2019-07-04 07:30:41.353][24][debug][pool] [external/envoy/source/common/http/http1/conn_pool.cc:164] [C121] purge pending, failure reason:
[2019-07-04 07:30:41.353][24][debug][router] [external/envoy/source/common/router/router.cc:644] [C119][S9661729384515860777] upstream reset: reset reason connection failure
[2019-07-04 07:30:41.353][24][trace][http] [external/envoy/source/common/http/conn_manager_impl.cc:1200] [C119][S9661729384515860777] encode headers called: filter=0x4f0e5f0 status=0
[2019-07-04 07:30:41.353][24][trace][http] [external/envoy/source/common/http/conn_manager_impl.cc:1200] [C119][S9661729384515860777] encode headers called: filter=0x4f0edc0 status=0
[2019-07-04 07:30:41.353][24][debug][filter] [src/envoy/http/mixer/filter.cc:133] Called Mixer::Filter : encodeHeaders 2
[2019-07-04 07:30:41.353][24][trace][http] [external/envoy/source/common/http/conn_manager_impl.cc:1200] [C119][S9661729384515860777] encode headers called: filter=0x4f0f0e0 status=0
[2019-07-04 07:30:41.353][24][debug][http] [external/envoy/source/common/http/conn_manager_impl.cc:1305] [C119][S9661729384515860777] encoding headers via codec (end_stream=false):
':status', '503'
'content-length', '91'
'content-type', 'text/plain'
'date', 'Thu, 04 Jul 2019 07:30:41 GMT'
'server', 'istio-envoy'
</code></pre>

<p>Has anyone encountered such an issue ? If you need more info about the configuration, I can provide.</p>

<p>Thanks for your answer Manvar. There was no problem with the curl enabled pod but thanks for the insight. It was a misconfiguration of our tomcat port that was not matching the service/virtualService config.</p>
