No connection to Mosquitto with localhost (Docker)

General
1

First of all, I must apologize, as this topic is most likely not directly related to Node-RED, but to Docker. But maybe you guys can help me anyway.

Node-RED is natively installed on a Raspberry Pi.
In parallel, an instance of Mosquitto is running in a Docker container.

I was always able to access the Mosquitto MQTT broker with localhost.

But after I had to completely rebuild the RPi, the connection only works via the real IP, i.e. 192.168.0.10 instead of also via localhost.
Unfortunately, I have absolutely no idea whether I have made a special setting for this, or whether this had worked out of the box.

I would rather not run the container on the network "host" on Docker.
This would allow me to address Mosquitto via localhost, but I'm sure I hadn't done it that way before the reinstall.

I would be very grateful for any tips and tricks.

Thanks a lot
Newbow

2

Why run mosquitto in a container in the first place... ?

3

Well, I thought this is the best way to handle updates.
I have serveral container and it's way easier to move/ clone container to another machine.

4

I just tried the IP 127.0.0.1 and it works... But why does it not work when using the word "localhost"? It used to work earlier. I don't get it.

5

What is in the file /etc/hosts?

6

This is my /etc/hosts:

127.0.0.1 localhost
::1 localhost ip6-localhost ip6-loopback
ff02::1 ip6-allnodes
ff02::2 ip6-allrouters
127.0.1.1 raspberrypi

7

In that case localhost should map to 127.0.0.1, so I don't know why that would not work. I suspect it is to do with the way the docker container is setup, but I don't know what. Unless it is an ipv6 issue.

8

Thank you Colin, you have put me on the right track.

I changed/ commented my /etc/hosts file as follows:

127.0.0.1 localhost
#::1 localhost ip6-localhost ip6-loopback
#ff02::1 ip6-allnodes
#ff02::2 ip6-allrouters
127.0.1.1 raspberrypi

I read somewhere that especially the localhost in the line:
::1 localhost ip6-localhost ip6-loopback causes problems.
Now it's working like a charm again. Maybe the ip6 crap got in my way :wink:

grafik

grafik

EDIT:
By the way, this also works (removing just the localhost in the second line):

127.0.0.1 localhost
#::1 localhost ip6-localhost ip6-loopback
::1 ip6-localhost ip6-loopback
ff02::1 ip6-allnodes
ff02::2 ip6-allrouters
127.0.1.1 raspberrypi

9

Normally what you have would work. Perhaps your docker container is not able to receive IPV6.

10

we have seen/heard of several issue with DNS and IPv6 on docker on Alpine builds (that we use).