Why can't i attach a container to a docker network? - docker

Question

I've created a user defined attachable overlay swarm network. I can inspect it, but when i attempt to attach a container to it, i get the following error when running on the manager node:
$ docker network connect mrunner baz
Error response from daemon: network mrunner not found
The network is defined and is attachable
$ docker network inspect mrunner
[
{
"Name": "mrunner",
"Id": "kviwxfejsuyc9476eznb7a8yw",
"Created": "2019-06-20T21:25:45.271304082Z",
"Scope": "swarm",
"Driver": "overlay",
"EnableIPv6": false,
"IPAM": {
"Driver": "default",
"Options": null,
"Config": [
{
"Subnet": "10.0.1.0/24",
"Gateway": "10.0.1.1"
}
]
},
"Internal": false,
"Attachable": true,
"Ingress": false,
"ConfigFrom": {
"Network": ""
},
"ConfigOnly": false,
"Containers": null,
"Options": {
"com.docker.network.driver.overlay.vxlanid_list": "4098"
},
"Labels": null
}
]
$ docker network ls
NETWORK ID NAME DRIVER SCOPE
4a454d677dea bridge bridge local
95383b47ee94 docker_gwbridge bridge local
249684755b51 host host local
zgx0nppx33vj ingress overlay swarm
kviwxfejsuyc mrunner overlay swarm
a30a12f8d7cc none null local
uftxcaoz9rzg taskman_default overlay swarm
Why is this network connection failing?
** This was answered here: https://github.com/moby/moby/issues/39391

Answer 1

See this:
To create an overlay network for use with swarm services, use a command like the following:
$ docker network create -d overlay my-overlay
To create an overlay network which can be used by swarm services or standalone containers to communicate with other standalone containers running on other Docker daemons, add the --attachable flag:
$ docker network create -d overlay --attachable my-attachable-overlay
So, by default overlay network cannot be used by standalone containers, if insist on, you need to add --attachable to allow this network be used by standalone containers.

Answer 2

Thanks to thaJeztah on docker git repo:
The solution is as follows, but essentially make the flow service centric:
docker network create -d overlay --attachable --scope=swarm somenetwork
docker service create --name someservice nginx:alpine
If you want to connect the service to the somenetwork after it was created, update the service;
docker service update --network-add somenetwork someservice
After this; all tasks of the someservice service will be connected to somenetwork (in addition to other overlay networks they were connected to).
https://github.com/moby/moby/issues/39391#issuecomment-505050610