dns-cache image mentioned in the docker swarm tutorial is not available

[digitzh]

Is this a docs issue?

• [X] My issue is about the documentation content or website

Type of issue

I can't find what I'm looking for

Description

The dns-cache docker image mentioned in the docker swarm's routing mesh tutorial doesn't seem to be available in the Docker Hub. Hence, creating a service using the commands mentioned in the docs, fails to create the containers. By listing down the containers of the service using docker service ps dns-cache, shows that the container shutdown with the error No such image: dns-cache:latest. Please look at the below information.

[user@zh-centos7 ~]$ docker service ps dns-cache
ID             NAME                                      IMAGE              NODE         DESIRED STATE   CURRENT STATE             ERROR                               PORTS
ir64yrpn16yq   dns-cache.7hlvcv20c6oc9350un75my54c       dns-cache:latest   zh-ubuntu    Ready           Preparing 2 seconds ago                                       
spkj7ux8eo1g    \_ dns-cache.7hlvcv20c6oc9350un75my54c   dns-cache:latest   zh-ubuntu    Shutdown        Rejected 3 seconds ago    "No such image: dns-cache:late…"   
nmsyn0j4fhan    \_ dns-cache.7hlvcv20c6oc9350un75my54c   dns-cache:latest   zh-ubuntu    Shutdown        Rejected 8 seconds ago    "No such image: dns-cache:late…"   
o57jt29a12ne    \_ dns-cache.7hlvcv20c6oc9350un75my54c   dns-cache:latest   zh-ubuntu    Shutdown        Rejected 13 seconds ago   "No such image: dns-cache:late…"   
qgsye6qlftje    \_ dns-cache.7hlvcv20c6oc9350un75my54c   dns-cache:latest   zh-ubuntu    Shutdown        Rejected 17 seconds ago   "No such image: dns-cache:late…"   
j1pm6r2d7hoh   dns-cache.qmx84ycynxfmzf27al9rttlp7       dns-cache:latest   zh-centos7   Ready           Preparing 4 seconds ago                                       
adb5ca1lk22c    \_ dns-cache.qmx84ycynxfmzf27al9rttlp7   dns-cache:latest   zh-centos7   Shutdown        Rejected 4 seconds ago    "No such image: dns-cache:late…"   
8kgndzb8m8ry    \_ dns-cache.qmx84ycynxfmzf27al9rttlp7   dns-cache:latest   zh-centos7   Shutdown        Rejected 15 seconds ago   "No such image: dns-cache:late…"   
i4wuq7mfz5nd    \_ dns-cache.qmx84ycynxfmzf27al9rttlp7   dns-cache:latest   zh-centos7   Shutdown        Rejected 21 seconds ago   "No such image: dns-cache:late…"   
o4t48st6k4yh    \_ dns-cache.qmx84ycynxfmzf27al9rttlp7   dns-cache:latest   zh-centos7   Shutdown        Rejected 27 seconds ago   "No such image: dns-cache:late…"   

Location

https://docs.docker.com/engine/swarm/ingress/#publish-a-port-for-tcp-only-or-udp-only

Suggestion

dns-cache image is not available in the Docker Hub. This issue is reported before, but didn't solve: https://github.com/docker/docs/issues/14287

[thaJeztah]

Thanks for reporting; I see that other ticket was closed by the stale-bot (which was sometimes a bit over-enthusiastic)

Looking at this example, I see those were introduced in https://github.com/docker/docs/pull/733, and from the context on that PR, I think the dns-cache image-name was intended to be "for illustrational purposes".

We should probably change the name of that image for something that's more clearly standing out as "not a real image name". Either that or an actual image providing UDP connections (from the looks of that example, it may be good to have something other than port 53 (DNS).

/cc @dvdksn

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