"Failed to establish a new connection" Azure App Service

Question

We have a custom Docker image that runs a Tomcat and exposes port 7000 to handle traffic. We store this image in a container registry accessible from our Azure subscription.

We deploy the image using Azure App Service and use the WEBSITES_PORT configuration to bind the port 7000. However, the App Service fails to start with the following error in the App Service logs

Exception in thread Thread-1:
Traceback (most recent call last):
  File "/usr/lib64/az/lib/python3.6/site-packages/urllib3/connection.py", line 175, in _new_conn
    (self._dns_host, self.port), self.timeout, **extra_kw
  File "/usr/lib64/az/lib/python3.6/site-packages/urllib3/util/connection.py", line 96, in create_connection
    raise err
  File "/usr/lib64/az/lib/python3.6/site-packages/urllib3/util/connection.py", line 86, in create_connection
    sock.connect(sa)
OSError: [Errno 113] No route to host
During handling of the above exception, another exception occurred:
Traceback (most recent call last):
  File "/usr/lib64/az/lib/python3.6/site-packages/urllib3/connectionpool.py", line 706, in urlopen
    chunked=chunked,
  File "/usr/lib64/az/lib/python3.6/site-packages/urllib3/connectionpool.py", line 382, in _make_request
    self._validate_conn(conn)
  File "/usr/lib64/az/lib/python3.6/site-packages/urllib3/connectionpool.py", line 1010, in _validate_conn
    conn.connect()
  File "/usr/lib64/az/lib/python3.6/site-packages/urllib3/connection.py", line 358, in connect
    conn = self._new_conn()
  File "/usr/lib64/az/lib/python3.6/site-packages/urllib3/connection.py", line 187, in _new_conn
    self, "Failed to establish a new connection: %s" % e
urllib3.exceptions.NewConnectionError: 

Answer 1

@Bera, Aniruddha (GE Healthcare, consultant) In addition to the helpful answer shared by Anonymous, I wanted to share some further suggestions that might be helpful.

It seems like your Azure App Service is failing to start with the error message "Failed to establish a new connection". The error message indicates that the App Service is unable to connect to the container registry where your custom Docker image is stored.

This could be due to a few reasons such as incorrect registry path name, incorrect credentials, or the container registry is behind a virtual network using a private endpoint in an unsupported region.

To troubleshoot this issue, you can try the following steps:

1. Check that the path name to your container registry is correct. For a registry my-registry.io and image test/image with tag 3.2, a valid image path would be my-registry.io/test/image:3.2. You can refer to the registry path documentation for more information.
2. Ensure that you have provided the correct credentials for the private registry you're trying to pull the image from.
3. If the container registry is behind a virtual network, ensure that it is using a private endpoint in a supported region. You can refer to the list of supported regions for more information.

Answer 2

change the internal port of docker container

docker build -f Dockerfile -t test/tomcat-test:1.0 .
docker run -d -p 4287:4287 --name tomcat-test test/tomcat-test:1.0

build the image and run