Bug 1570398 - [3.9] DNS to local node vs. static egress IP
Summary: [3.9] DNS to local node vs. static egress IP
Keywords:
Status: CLOSED ERRATA
Alias: None
Product: OpenShift Container Platform
Classification: Red Hat
Component: Networking
Version: 3.9.0
Hardware: x86_64
OS: Linux
medium
medium
Target Milestone: ---
: 3.9.z
Assignee: Dan Winship
QA Contact: Meng Bo
URL:
Whiteboard:
Depends On: 1557924
Blocks:
TreeView+ depends on / blocked
 
Reported: 2018-04-22 14:59 UTC by Dan Winship
Modified: 2018-12-29 03:43 UTC (History)
2 users (show)

Fixed In Version:
Doc Type: Bug Fix
Doc Text:
Cause: When using per-namespace static egress IPs, all external traffic is routed through the egress IP. "External" means all traffic which isn't directed to another pod, and so includes traffic from the pod to the pod's node. Consequence: When pods are told to use the node's IP address for DNS, and the pod is using a static egress IP, then DNS traffic will be routed to the egress node first, and then back to the original node, which might be configured to not accept DNS requests from other hosts, causing the pod to be unable to resolve DNS. Fix: pod-to-node DNS requests now bypass the egress IP and go directly to the node Result: DNS works
Clone Of: 1557924
: 1570399 1570400 (view as bug list)
Environment:
Last Closed: 2018-05-17 06:43:40 UTC
Target Upstream Version:

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Links
System ID Private Priority Status Summary Last Updated
Github ose/pull/1218 0 None None None 2018-04-22 15:02:29 UTC
Red Hat Product Errata RHBA-2018:1566 0 None None None 2018-05-17 06:44:00 UTC

Comment 1 Dan Winship 2018-04-22 15:02:30 UTC 
https://github.com/openshift/ose/pull/1218
Comment 5 Meng Bo 2018-05-02 09:22:31 UTC 
Tested on build v3.9.27

The dns query on a non-egress-node pod will not be transferred to the egress node.

Steps:
1. Setup env with network policy plugin
2. Patch any of the node as egress node
3. Create project and pods in it
4. Patch project with egress IP in step 2
5. tcpdump on port 53 on all the nodes
6. Try to send a dns query to the local dns server from the pod which is landed on the non-egress-node 
7. There is no packet generated on the egress node
Comment 6 Dan Winship 2018-05-02 11:57:46 UTC 
(In reply to Meng Bo from comment #5)
> 6. Try to send a dns query to the local dns server from the pod which is
> landed on the non-egress-node 
> 7. There is no packet generated on the egress node

(And the DNS query in step 6 should succeed.)
Comment 7 Meng Bo 2018-05-03 02:46:11 UTC 
(In reply to Dan Winship from comment #6)
> (In reply to Meng Bo from comment #5)
> > 6. Try to send a dns query to the local dns server from the pod which is
> > landed on the non-egress-node 
> > 7. There is no packet generated on the egress node
> 
> (And the DNS query in step 6 should succeed.)

Aha, yeah, thanks.
It succeeded indeed.
Comment 10 errata-xmlrpc 2018-05-17 06:43:40 UTC 
Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.

For information on the advisory, and where to find the updated
files, follow the link below.

If the solution does not work for you, open a new bug report.

https://access.redhat.com/errata/RHBA-2018:1566
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