Service links don't work within kubernetes pods

[solsson]

By design we call svn -> rweb -> svn to serve ?rweb= stuff. With docker-compose this works if services are named like that, or one of them is and the other has a links: entry.

For example the svn container tends to respond Proxy Error DNS lookup failure for: rweb if the following strings don't match:

• https://github.com/Reposoft/docker-svn/blob/v0.6.0/build-contracts/docker-compose.yml#L4
• https://github.com/Reposoft/docker-svn/blob/v0.6.0/build-contracts/docker-compose.yml#L32
• https://github.com/Reposoft/rweb/blob/v1.6.0/test/conf-svn/rweb-services.conf#L16

In Kubernetes you typically run svn and rweb containers in the same pod, which means that svn will reach rweb on 127.0.0.1:9000, but not rweb:9000.

[solsson]

By the way why is there double slashes after rweb:9000 in services.conf?

[solsson]

Can individual containers be resolved by name in Kubernetes pods? The most elegant solution to this issue would be that svn:80 and rweb:9000 works in both docker-compose and kube.

[solsson]

Using this workaround in a downstream dockerfile specifically for kubernetes:

RUN  sed -i 's|fcgi://rweb:9000|fcgi://127.0.0.1:9000|' conf/svn/rweb/services-fpm.conf \
  && sed -i 's|fcgi://rweb:9000|fcgi://127.0.0.1:9000|' conf/svn/rweb/load-fpm.conf

The RWEB_SVC variable i conf/svn/rweb/services-fpm.conf is no solution because ProxyPassMatch doesn't support variables. Maybe if we use rewrite there too. Name resolution would be more elegant though.

[solsson]

Improved the workaround so that it can work with regular docker, given a named link.

diff --git a/build-contracts/docker-compose.yml b/build-contracts/docker-compose.yml
index ea08931..2244d33 100644
--- a/build-contracts/docker-compose.yml
+++ b/build-contracts/docker-compose.yml
@@ -9,6 +9,8 @@ services:
     environment:
       - DEBUG=true
       - REPOS_SVC=fcgi://rweb:9000/opt/rweb
+    links:
+      - rweb:svn
   rweb:
     image: solsson/rweb:latest
     expose:
diff --git a/rweb-svn/Dockerfile b/rweb-svn/Dockerfile
index e77ba2b..6338dad 100644
--- a/rweb-svn/Dockerfile
+++ b/rweb-svn/Dockerfile
@@ -7,5 +7,5 @@ ADD leansetup /usr/local/bin/
 RUN sed -i 's/set -e/set -e\n\nleansetup/' /usr/local/bin/httpd-foreground

 # fix multi-container pod issue "DNS lookup failure for: rweb"
-RUN  sed -i 's|fcgi://rweb:9000|fcgi://127.0.0.1:9000|' conf/svn/rweb/services-fpm.conf \
-  && sed -i 's|fcgi://rweb:9000|fcgi://127.0.0.1:9000|' conf/svn/rweb/load-fpm.conf
+RUN  sed -i 's|fcgi://rweb:9000|fcgi://svn:9000|' conf/svn/rweb/services-fpm.conf \
+  && sed -i 's|fcgi://rweb:9000|fcgi://svn:9000|' conf/svn/rweb/load-fpm.conf

As the commit comment says I also tried the name _rweb._tcp.svn (see http://kubernetes.io/docs/admin/dns/#srv-records) but got DNS lookup failure for: _rweb._tcp.svn. I'm guessing that apache's name lookup doesn't support this dns extension.

[solsson]

I don't know what commit I'm referring to above, but now I realize that this isn't a problem with the docker image. Instead, in kubernetes, add a headless service rweb alongside your svn service, and the internal proxy httpd->fpm will work just like in docker-compose. For example, with the same selector app: svn that the service uses:

apiVersion: v1
kind: Service
metadata:
  name: rweb
spec:
  clusterIP: None
  selector:
    app: svn
  ports:
  - port: 9000
    targetPort: 9000

For more info see: https://kubernetes.io/docs/user-guide/services/#headless-services