Docker swarm overlay, single node, no connection between services - docker

Question

I'm trying to make a connection from one service to another, to achieve it I created an overlay network and two services attached to it like so.
$ docker network create -d overlay net1
$ docker service create --name busybox --network net1 busybox sleep 3000
$ docker service create --name busybox2 --network net1 busybox sleep 3000
Now I make sure my services are running and both connected to overlay.
$ docker ps
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
ecc8dd465cb1 busybox:latest "sleep 3000" About a minute ago Up About a minute busybox2.1.uw597s90tkvbcaisgaq7los2q
f8cfe793e3d9 busybox:latest "sleep 3000" About a minute ago Up About a minute busybox.1.l5lxp4v0mcbujqh79dne2ds42
$ docker network inspect net1
[
{
"Name": "net1",
"Id": "5dksx8hlxh1rbj42pva21obyz",
"Created": "2021-06-22T14:23:43.739770415Z",
"Scope": "swarm",
"Driver": "overlay",
"EnableIPv6": false,
"IPAM": {
"Driver": "default",
"Options": null,
"Config": [
{
"Subnet": "10.0.4.0/24",
"Gateway": "10.0.4.1"
}
]
},
"Internal": false,
"Attachable": false,
"Ingress": false,
"ConfigFrom": {
"Network": ""
},
"ConfigOnly": false,
"Containers": {
"ecc8dd465cb12c622f48b109529534279dddd4fe015a66c848395157fb73bc69": {
"Name": "busybox2.1.uw597s90tkvbcaisgaq7los2q",
"EndpointID": "b666f6374a815341cb8af7642a7523c9bb153f153b688218ad006605edd6e196",
"MacAddress": "02:42:0a:00:04:06",
"IPv4Address": "10.0.4.6/24",
"IPv6Address": ""
},
"f8cfe793e3d97f72393f556c2ae555217e32e35b00306e765489ac33455782aa": {
"Name": "busybox.1.l5lxp4v0mcbujqh79dne2ds42",
"EndpointID": "fff680bd13a235c4bb050ecd8318971612b66954f7bd79ac3ee0799ee18f16bf",
"MacAddress": "02:42:0a:00:04:03",
"IPv4Address": "10.0.4.3/24",
"IPv6Address": ""
},
"lb-net1": {
"Name": "net1-endpoint",
"EndpointID": "2a3b02f66f395e613c6bc88f16d0723762d28488b429a9e50f7df24c04e9f1f0",
"MacAddress": "02:42:0a:00:04:04",
"IPv4Address": "10.0.4.4/24",
"IPv6Address": ""
}
},
"Options": {
"com.docker.network.driver.overlay.vxlanid_list": "4101"
},
"Labels": {},
"Peers": [
{
"Name": "e1c2ac76b95b",
"IP": "10.18.0.6"
}
]
}
]
So far so good! Next I ssh into one of containers and try to nslookup the second one, but have no luck.
$ docker exec -it busybox.1.l5lxp4v0mcbujqh79dne2ds42 sh
/ # nslookup busybox2
Server: 127.0.0.11
Address: 127.0.0.11:53
Non-authoritative answer:
*** Can't find busybox2: No answer
*** Can't find busybox2: No answer
/ # nslookup busybox2.1.uw597s90tkvbcaisgaq7los2q
Server: 127.0.0.11
Address: 127.0.0.11:53
Non-authoritative answer:
*** Can't find busybox2.1.uw597s90tkvbcaisgaq7los2q: No answer
*** Can't find busybox2.1.uw597s90tkvbcaisgaq7los2q: No answer
I know that overlay questions are quite common here, but they are mostly about node to node connections, not single node swarm. Another think to keep in mind is there is no local firewall on that node at all.
Am I trying to connect in the wrong way or is it a configuration issue?

Answer 1

The solution was simply adding a --attachable flag to network create command. After that I could ping my services by name.
Turns out you need that flag no matter if you are adding stack (in my case I have multiple stacks in the same swarm) or single services.

Answer 2

docker service create ... --network net1 does not create network aliases by default. To get that behaviour you need to use the long form syntax of --network
docker service create --network name=net1,alias=busybox1 busybox tail -f /dev/null
Its interesting that making the network attachable has a similar effect. Usually a network is made attachable so that containers can be attached to it via docker run --network net1 ... so while this approach works, it has potentially undesirable side effects for whatever network attachability is supposed to protect against.