Question: We can use below syntax in Dockerfile for HTTP healthcheck . 

```
HEALTHCHECK --interval=5s --timeout=3s CMD curl --fail      http://localhost/feeds/check || exit 1

```

I want to know what if i want to use a TCP healthcheck ? 

PS- Not sure if docker supports it natively & we don't need any extra configuration for that .

Answer: 
Docker healthcheck's are implemented by running any command you give it inside the container and checking the return code. So if, for example, you install curl and jq, you can parse the output of some json to determine the health.

For your tcp port, just include the needed executables inside your image, and the command to run to test it as your healthcheck. That executable may be your application client, could be netstat to check if the port is listening, or it could be net cat to implement your own manual test.
HTTP designed to works over TCP protocol only, thus HTTP healthcheck will reflect health of TCP link.