Timofey Barmin: did you test this on a Linux machine by using sysctl to disable the IPv6 stack? Is it the case that the system can't be started on a machine with the IPv6 stack disabled?

I emulated error from inet6_tcp_dist:listen(). In this case the problem occurs.

Dave Finlay
> Is it the case that the system can't be started on a machine with the IPv6 stack disabled?
It can be started, but it can't be initialized using UI. I didn't test initialization using CLI for this particular case, but most likely the behavior will be the same.

After discussion I reproduced it on ubuntu 16.04 vagrant machine using the following steps:
1) Disable ipv6 in grub configuration in /etc/default/grub:
GRUB_CMDLINE_LINUX_DEFAULT="ipv6.disable=1"
2) sudo update-grub
3) restart the machine
4) install couchbase package
5) try to initialize the node using UI (ipv6 checkbox is unchecked)
6) after pressing "Save and Finish" node doesn't respond

If cluster is initialized using CLI command the problem only happen when --ipv4 is specified explicitly:
For example:
The following command breaks the node when IPv6 is not available

couchbase-cli node-init -c 127.0.0.1:9000 -u Administrator -p asdasd --node-init-hostname node0.localhost --ipv4

but this command doesn't break it the initialization completes successfully:

couchbase-cli node-init -c 127.0.0.1:9000 -u Administrator -p asdasd --node-init-hostname node0.localhost

Timofey - thank you for this - this is very clear.

Ritam Sharma: I think you are testing nodes with the IPv6 stack disabled / not available. Can you confirm? Is it the case that you were testing this with the REST API or CLI and not explicitly specifying the --ipv4 parameter?

At any rate, it's clear for me that this is must-fix. Approving for inclusion in Mad Hatter.

Build couchbase-server-6.5.0-4922 contains ns_server commit 6790138 with commit message:
MB-37138: Lighten listeners check up on cb_dist config update

Dave Finlay - No, not at ipv6 disabled at stack level. Similar issue was raised for 5.5 - https://issues.couchbase.com/browse/MB-30610

Normal configuration for the boxes that I have is follows:

eth0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500

        inet 172.23.97.52  netmask 255.255.252.0  broadcast 172.23.99.255

        inet6 fe80::f84e:67ff:febd:e4d0  prefixlen 64  scopeid 0x20<link>

        inet6 fd63:6f75:6368:2060:f84e:67ff:febd:e4d0  prefixlen 64  scopeid 0x0<global>

        ether fa:4e:67:bd:e4:d0  txqueuelen 1000  (Ethernet)

        RX packets 6371215  bytes 2714317585 (2.5 GiB)

        RX errors 0  dropped 0  overruns 0  frame 0

        TX packets 5122512  bytes 5523467629 (5.1 GiB)

        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

lo: flags=73<UP,LOOPBACK,RUNNING>  mtu 65536

        inet 127.0.0.1  netmask 255.0.0.0

        inet6 ::1  prefixlen 128  scopeid 0x10<host>

        loop  txqueuelen 1000  (Local Loopback)

        RX packets 6354520  bytes 4149356362 (3.8 GiB)

        RX errors 0  dropped 0  overruns 0  frame 0

        TX packets 6354520  bytes 4149356362 (3.8 GiB)

        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

Build couchbase-server-6.5.0-4926 contains ns_server commit 3327aac with commit message:
MB-37138: Show error message in UI if configuration of ...

Build couchbase-server-7.0.0-1135 contains ns_server commit 3327aac with commit message:
MB-37138: Show error message in UI if configuration of ...

Build couchbase-server-7.0.0-1135 contains ns_server commit 6790138 with commit message:
MB-37138: Lighten listeners check up on cb_dist config update