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Re: Question about Openshift origin DNS



Hi Scott,

Thanks for your response.

My cluster infrastructure is as below,

10.1.241.54 lb

10.1.236.92/93  master

10.1.241.55/56  work nodes

All the machines are VMs provisioned by OpenStack.

I tried to run "dig redis-svc.redis.svc.cluster.local" on all the nodes.

The instruction failed on node 10.1.236.92.  But service dnsmasq is running on the host node.

Why did the instruction only fail on this node?


Another question is about dns name of the container.

In my test case, there is one pod which has two containers named "master" and "sentinel".

[root host-10-1-236-93 ~]# oc get pods -n redis -o wide
NAME                         READY     STATUS    RESTARTS   AGE       IP           NODE
sb-2017-redis-master-qp13j   2/2       Running   0          14m       10.130.0.3   host-10-1-241-55
And following operations failed with error reason "connection timed out; no servers could be reached".

dig sb-2017-redis-master-qp13j.redis.cluster.local

dig master.sb-2017-redis-master-qp13j.redis.cluster.local

dig master.sb-2017-redis-master-qp13j.cluster.local

dig master.redis.cluster.local


Could containers be find by dns name with the format <container name>.<pod_namespace>.cluster.local?


I followed the document via https://docs.openshift.org/1.5/architecture/additional_concepts/networking.html.

Is there any misunderstanding about this?

However, it seems that dns name of svc and endpoints works for me.


Thanks,

Jared, (韦煜)
Software developer
Interested in open source software, big data, Linux


From: Scott Dodson <sdodson redhat com>
Sent: Monday, August 21, 2017 9:10:44 PM
To: Yu Wei
Cc: users lists openshift redhat com; dev lists openshift redhat com
Subject: Re: Question about Openshift origin DNS
 
10.1.241.55 should be the IP address of the node and dnsmasq should be running on the node which will route queries for 'cluster.local' to the appropriate place. Can you check on dnsmasq on the node?

On Mon, Aug 21, 2017 at 6:38 AM, Yu Wei <yu2003w hotmail com> wrote:

Hi,

I setup Openshift Origin 1.5 with openvswitch network plugin.

It seemed that dns server setup was not properly within pod.

services, endpoints couldn't be reached by name.

Within pod, /etc/resolv.conf contains following content,

root sb-2017-redis-master-w7g44:/data# cat /etc/resolv.conf
search redis.svc.cluster.local svc.cluster.local cluster.local
nameserver 10.1.241.55
options ndots:5


Then I added "172.30.0.1" to /etc/resolv.conf as below,

root sb-2017-redis-master-w7g44:/data# cat /etc/resolv.conf
search redis.svc.cluster.local svc.cluster.local cluster.local
nameserver 10.1.241.55
options ndots:5
nameserver 172.30.0.1

Then services, endpoints could be found by dns name.

So why is "nameserver 172.30.0.1" not added to /etc/resolv.conf automatically?

Did I missed anything when setup cluster?



[root host-10-1-236-92 gluster]# dig redis-svc.redis.svc.cluster.local

; <<>> DiG 9.9.4-RedHat-9.9.4-29.el7 <<>> redis-svc.redis.svc.cluster.local
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 4207
;; flags: qr aa rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 0

;; QUESTION SECTION:
;redis-svc.redis.svc.cluster.local. IN    A

;; ANSWER SECTION:
redis-svc.redis.svc.cluster.local. 30 IN A    172.30.4.92

;; Query time: 2 msec
;; SERVER: 172.30.0.1#53(172.30.0.1)
;; WHEN: Mon Aug 21 18:48:50 CST 2017
;; MSG SIZE  rcvd: 67

[root host-10-1-236-92 gluster]# dig redis-svc.redis.endpoints.cluster.local

; <<>> DiG 9.9.4-RedHat-9.9.4-29.el7 <<>> redis-svc.redis.endpoints.cluster.local
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 19434
;; flags: qr aa rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 0

;; QUESTION SECTION:
;redis-svc.redis.endpoints.cluster.local. IN A

;; ANSWER SECTION:
redis-svc.redis.endpoints.cluster.local. 30 IN A 10.130.0.2

;; Query time: 5 msec
;; SERVER: 172.30.0.1#53(172.30.0.1)
;; WHEN: Mon Aug 21 18:49:05 CST 2017
;; MSG SIZE  rcvd: 73







Thanks,

Jared, (韦煜)
Software developer
Interested in open source software, big data, Linux


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