Google App Engine Docker Container 502 Bad Gateway - wordpress

Question

I am trying to deploy my docker image to google app engine, I succfully mananged to build the image and push it to GCR. And deploy it using gcloud app deploy --image 'link-to-image-on-gcr'
But when accessing the application I'm getting a 502 bad gateway. I ssh into the server and checked the logs of the nginx container in docker and discovered the below log
2020/05/04 00:52:50 [error] 33#33: *127 connect() failed (111: Connection refused) while connecting to upstream, client: 74.125.24.153, server: , request: "GET /wp-login.php HTTP/1.1", upstream: "http://172.17.0.1:8080/wp-login.php", host: "myappengineservice-myrepo.ue.r.appspot.com"
By default, my docker image only has one container (its a Wordpress image), when deployed to app engine I suppose by default app engine will start my docker container within docker and expose the frontend via an Nginx proxy, so all the requests are routed through the Nginx proxy.
After playing around for a while, I edited the Nginx configuration file and came across this line
location / {
proxy_pass http://app_server;
I edited this a replaced it with my Wordpress docker containers internal IP address.
(proxy_pass http://172.17.0.6;)
And voila it seemed to have worked, and the requests are now been routed to my docker container.
This was obviously a temporary fix, how can I make this permanent and any idea on why this is happening?
app.yaml
runtime: custom
service: my-wordpress
env: flex
nginx.conf (inside the Nginx container)
daemon off;
worker_processes auto;
events {
worker_connections 4096;
multi_accept on;
}
http {
include mime.types;
server_tokens off;
variables_hash_max_size 2048;
# set max body size to 32m as appengine supports.
client_max_body_size 32m;
tcp_nodelay on;
tcp_nopush on;
underscores_in_headers on;
# GCLB uses a 10 minutes keep-alive timeout. Setting it to a bit more here
# to avoid a race condition between the two timeouts.
keepalive_timeout 650;
# Effectively unlimited number of keepalive requests in the case of GAE flex.
keepalive_requests 4294967295;
upstream app_server {
keepalive 192;
server gaeapp:8080;
}
geo $source_type {
default ext;
127.0.0.0/8 lo;
169.254.0.0/16 sb;
35.191.0.0/16 lb;
130.211.0.0/22 lb;
172.16.0.0/12 do;
}
map $http_upgrade $ws_connection_header_value {
default "";
websocket upgrade;
}
# ngx_http_realip_module gets the second IP address from the last of the X-Forwarded-For header
# X-Forwarded-For: [USER REQUEST PROVIDED X-F-F.]USER-IP.GCLB_IP
set_real_ip_from 0.0.0.0/0;
set_real_ip_from 0::/0;
real_ip_header X-Forwarded-For;
iap_jwt_verify off;
iap_jwt_verify_project_number 96882395728;
iap_jwt_verify_app_id my-project-id;
iap_jwt_verify_key_file /iap_watcher/iap_verify_keys.txt;
iap_jwt_verify_iap_state_file /iap_watcher/iap_state;
iap_jwt_verify_state_cache_time_sec 300;
iap_jwt_verify_key_cache_time_sec 43200;
iap_jwt_verify_logs_only on;
server {
iap_jwt_verify on;
# self signed ssl for load balancer traffic
listen 8443 default_server ssl;
ssl_certificate /etc/ssl/localcerts/lb.crt;
ssl_certificate_key /etc/ssl/localcerts/lb.key;
ssl_protocols TLSv1.2;
ssl_ciphers EECDH+AES256:!SHA1;
ssl_prefer_server_ciphers on;
ssl_session_timeout 3h;
proxy_pass_header Server;
gzip on;
gzip_proxied any;
gzip_types text/html text/plain text/css text/xml text/javascript application/json application/javascript application/xml application/xml+rss application/protobuf application/x-protobuf;
gzip_vary on;
# Allow more space for request headers.
large_client_header_buffers 4 32k;
# Allow more space for response headers. These settings apply for response
# only, not requests which buffering is disabled below.
proxy_buffer_size 64k;
proxy_buffers 32 4k;
proxy_busy_buffers_size 72k;
# Explicitly set client buffer size matching nginx default.
client_body_buffer_size 16k;
# If version header present, make sure it's correct.
if ($http_x_appengine_version !~ '(?:^$)|(?:^my-wordpress:20200504t053100(?:\..*)?$)') {
return 444;
}
set $x_forwarded_for_test "";
# If request comes from sb, lo, or do, do not care about x-forwarded-for header.
if ($source_type !~ sb|lo|do) {
set $x_forwarded_for_test $http_x_forwarded_for;
}
# For local health checks only.
if ($http_x_google_vme_health_check = 1) {
set $x_forwarded_for_test "";
}
location / {
proxy_pass http://app_server;
proxy_redirect off;
proxy_http_version 1.1;
proxy_set_header Connection "";
proxy_set_header Host $host;
proxy_set_header X-Forwarded-Host $server_name;
proxy_send_timeout 3600s;
proxy_read_timeout 3600s;
proxy_set_header Upgrade $http_upgrade;
proxy_set_header Connection $ws_connection_header_value;
proxy_set_header X-AppEngine-Api-Ticket $http_x_appengine_api_ticket;
proxy_set_header X-AppEngine-Auth-Domain $http_x_appengine_auth_domain;
proxy_set_header X-AppEngine-BlobChunkSize $http_x_appengine_blobchunksize;
proxy_set_header X-AppEngine-BlobSize $http_x_appengine_blobsize;
proxy_set_header X-AppEngine-BlobUpload $http_x_appengine_blobupload;
proxy_set_header X-AppEngine-Cron $http_x_appengine_cron;
proxy_set_header X-AppEngine-Current-Namespace $http_x_appengine_current_namespace;
proxy_set_header X-AppEngine-Datacenter $http_x_appengine_datacenter;
proxy_set_header X-AppEngine-Default-Namespace $http_x_appengine_default_namespace;
proxy_set_header X-AppEngine-Default-Version-Hostname $http_x_appengine_default_version_hostname;
proxy_set_header X-AppEngine-Federated-Identity $http_x_appengine_federated_identity;
proxy_set_header X-AppEngine-Federated-Provider $http_x_appengine_federated_provider;
proxy_set_header X-AppEngine-Https $http_x_appengine_https;
proxy_set_header X-AppEngine-Inbound-AppId $http_x_appengine_inbound_appid;
proxy_set_header X-AppEngine-Inbound-User-Email $http_x_appengine_inbound_user_email;
proxy_set_header X-AppEngine-Inbound-User-Id $http_x_appengine_inbound_user_id;
proxy_set_header X-AppEngine-Inbound-User-Is-Admin $http_x_appengine_inbound_user_is_admin;
proxy_set_header X-AppEngine-QueueName $http_x_appengine_queuename;
proxy_set_header X-AppEngine-Request-Id-Hash $http_x_appengine_request_id_hash;
proxy_set_header X-AppEngine-Request-Log-Id $http_x_appengine_request_log_id;
proxy_set_header X-AppEngine-TaskETA $http_x_appengine_tasketa;
proxy_set_header X-AppEngine-TaskExecutionCount $http_x_appengine_taskexecutioncount;
proxy_set_header X-AppEngine-TaskName $http_x_appengine_taskname;
proxy_set_header X-AppEngine-TaskRetryCount $http_x_appengine_taskretrycount;
proxy_set_header X-AppEngine-TaskRetryReason $http_x_appengine_taskretryreason;
proxy_set_header X-AppEngine-Upload-Creation $http_x_appengine_upload_creation;
proxy_set_header X-AppEngine-User-Email $http_x_appengine_user_email;
proxy_set_header X-AppEngine-User-Id $http_x_appengine_user_id;
proxy_set_header X-AppEngine-User-Is-Admin $http_x_appengine_user_is_admin;
proxy_set_header X-AppEngine-User-Nickname $http_x_appengine_user_nickname;
proxy_set_header X-AppEngine-User-Organization $http_x_appengine_user_organization;
proxy_set_header X-AppEngine-Version "";
add_header X-AppEngine-Flex-AppLatency $request_time always;
}
include /var/lib/nginx/extra/*.conf;
}
server {
# expose /nginx_status but on a different port (8090) to avoid
# external visibility / conflicts with the app.
listen 8090;
location /nginx_status {
stub_status on;
access_log off;
}
location / {
root /dev/null;
}
}
server {
# expose health checks on a different port to avoid
# external visibility / conflicts with the app.
listen 10402 ssl;
ssl_certificate /etc/ssl/localcerts/lb.crt;
ssl_certificate_key /etc/ssl/localcerts/lb.key;
ssl_protocols TLSv1.2;
ssl_ciphers EECDH+AES256:!SHA1;
ssl_prefer_server_ciphers on;
ssl_session_timeout 3h;
location = /liveness_check {
if ( -f /tmp/nginx/lameducked ) {
return 503 'lameducked';
}
if ( -f /var/lib/google/ae/unhealthy/sidecars ) {
return 503 'unhealthy sidecars';
}
if ( !-f /var/lib/google/ae/disk_not_full ) {
return 503 'disk full';
}
if ( -f /tmp/nginx/app_lameducked ) {
return 200 'ok';
}
return 200 'ok';
}
location = /readiness_check {
if ( -f /tmp/nginx/lameducked ) {
return 503 'lameducked';
}
if ( -f /var/lib/google/ae/unhealthy/sidecars ) {
return 503 'unhealthy sidecars';
}
if ( !-f /var/lib/google/ae/disk_not_full ) {
return 503 'disk full';
}
if ( -f /tmp/nginx/app_lameducked ) {
return 503 'app lameducked';
}
return 200 'ok';
}
}
# Add session affinity entry to log_format line i.i.f. the GCLB cookie
# is present.
map $cookie_gclb $session_affinity_log_entry {
'' '';
default sessionAffinity=$cookie_gclb;
}
# Output nginx access logs in the standard format, plus additional custom
# fields containing "X-Cloud-Trace-Context" header, the current epoch
# timestamp, the request latency, and "X-Forwarded-For" at the end.
# If you make changes to the log format below, you MUST validate this against
# the parsing regex at:
# GoogleCloudPlatform/appengine-sidecars-docker/fluentd_logger/managed_vms.conf
# (In general, adding to the end of the list does not require a change if the
# field does not need to be logged.)
log_format custom '$remote_addr - $remote_user [$time_local] '
'"$request" $status $body_bytes_sent '
'"$http_referer" "$http_user_agent" '
'tracecontext="$http_x_cloud_trace_context" '
'timestampSeconds="${msec}000000" '
'latencySeconds="$request_time" '
'x-forwarded-for="$http_x_forwarded_for" '
'uri="$uri" '
'appLatencySeconds="$upstream_response_time" '
'appStatusCode="$upstream_status" '
'upgrade="$http_upgrade" '
'iap_jwt_action="$iap_jwt_action" '
'$session_affinity_log_entry';
access_log /var/log/nginx/access.log custom;
error_log /var/log/nginx/error.log warn;
}
/etc/hosts (inside Nginx container)
root#f9c9cb5df8e2:/etc/nginx# cat /etc/hosts
127.0.0.1 localhost
::1 localhost ip6-localhost ip6-loopback
fe00::0 ip6-localnet
ff00::0 ip6-mcastprefix
ff02::1 ip6-allnodes
ff02::2 ip6-allrouters
172.17.0.1 gaeapp
172.17.0.5 f9c9cb5df8e2
docker ps result

Answer 1

I was able to solve the issue by exposing my Wordpress site through port 8080 from my docker container, it was exposed through port 80 before. It does not make much sense but if anyone knows the roots cause, please do go ahead and explain.