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From an AWS ec2 instance (which runs docker), I am trying to curl my docker container-hosted web service.

Given:

[ec2-user]$ docker ps
CONTAINER ID        IMAGE                                                                COMMAND                  CREATED             STATUS              PORTS                                        NAMES
b56fa0d76d5c        $REGISTRY/$WORK/metrics:v0.1.0   "/bin/sh -c 'sh /root"   3 minutes ago       Up 3 minutes        0.0.0.0:80->80/tcp, 0.0.0.0:9000->9000/tcp   insane_leakey

I can hit the web service from within the container:

[ec2-user]$ docker exec -it b56fa0d76d5c bash
root@b56fa0d76d5c:/# curl 'http://localhost/health'
Request is missing required query parameter 'apiName'

But, I can't hit it from the host:

[ec2-user]$ curl 'http://localhost/health'
curl: (56) Recv failure: Connection reset by peer

I looked at this detailed answer on this curl error, but I'm not sure how to debug this issue.

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Kevin Meredith
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2 Answers2

33

Connection Reset to a Docker container usually indicates that you've defined a port mapping for the container that does not point to an application.

So, if you've defined a mapping of 80:80, check that your process inside the docker instance is in fact running on port 80:

netstat -an|grep LISTEN

You get a reset as the Docker 'proxy' picks up the connection, attempts to connect to the process inside the container, fails, so resets the connection.

Jason Martin
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10

You can investigate this by installing tshark on the container and then do tshark -i any:

If you then do a request externally you should see something like the below:

root@618910b515f0:/code# tshark -i any
Running as user "root" and group "root". This could be dangerous.
Capturing on 'any'
tshark: cap_set_proc() fail return: Operation not permitted

tshark: cap_set_proc() fail return: Operation not permitted


1 0.000000000   172.18.0.1 → 172.18.0.3   TCP 76 45844 → 8001 [SYN] Seq=0 Win=29200 Len=0 MSS=1460 SACK_PERM=1 TSval=820044004 TSecr=0 WS=128
2 0.000019457   172.18.0.3 → 172.18.0.1   TCP 56 8001 → 45844 [RST, ACK] Seq=1 Ack=1 Win=0 Len=0

The network packet came in but it responded with a RST, which means it was rejected.

Most probably you're listening on 127.0.0.1 rather than 0.0.0.0 - all IPs. You can verify this by running netstat -tulpn

Chris Stryczynski
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