Hi,
I am using GitLab CI/CD which generates container names in a very large format to ensure uniqueness across projects, pipelines, etc - e.g.:
runner-jl9klc-project-30504-concurrent-0-fd6217607b395033-build-3
Gitlab also provides aliases for these containers (e.g. build, mariadb, etc.)
I am trying to connect to a Java JMX/RMI interface which is hosted on another container in the same bridge network. Forward DNS lookups for the alias work correctly, but Java RMI security requires a reverse DNS lookup to authenticate the connection. In this case no response is received from Docker DNS:
nslookup build
Server: 127.0.0.11
Address: 127.0.0.11#53
Non-authoritative answer:
Name: build
Address: 172.18.0.2
.
nslookup 172.18.0.2
;; connection timed out; no servers could be reached
Looking into the docker daemon log I can see the following errors:
Apr 13 08:20:06 test-docker.novalocal dockerd[15371]: time="2021-04-13T08:20:06.417125309Z" level=debug msg="[resolver] lookup for IP 2.0.19.172: name runner-jl9klc-project-30504-concurrent-0-fd6217607b395033-build-3.runner-jl9klc-project-30504-concurrent-0-job-1297211-network"
Apr 13 08:20:06 test-docker.novalocal dockerd[15371]: time="2021-04-13T08:20:06.417150733Z" level=error msg="[resolver] error writing resolver resp, dns: bad rdata"
Through manual testing I was able to verify that reverse DNS fails once the container name is larger than 62 characters.
Unfortunately I believe this Gitlab CI Runner behaviour is hard-coded so cannot be configured to make the container names smaller. Is there something that can be done in docker to mitigate this issue?
OS: CentOS 7
Docker Version:
Server: Docker Engine - Community
Engine:
Version: 20.10.6
API version: 1.41 (minimum version 1.12)
Go version: go1.13.15
Git commit: 8728dd2
Built: Fri Apr 9 22:43:57 2021
OS/Arch: linux/amd64
Experimental: false
containerd:
Version: 1.4.4
GitCommit: 05f951a3781f4f2c1911b05e61c160e9c30eaa8e
runc:
Version: 1.0.0-rc93
GitCommit: 12644e614e25b05da6fd08a38ffa0cfe1903fdec
docker-init:
Version: 0.19.0
GitCommit: de40ad0
Curtis