| Summary: | [DOCS] [3.4] Document tuning options for arp cache | ||
|---|---|---|---|
| Product: | OpenShift Container Platform | Reporter: | Vikram Goyal <vigoyal> |
| Component: | Documentation | Assignee: | brice <bfallonf> |
| Status: | CLOSED CURRENTRELEASE | QA Contact: | Johnny Liu <jialiu> |
| Severity: | medium | Docs Contact: | Vikram Goyal <vigoyal> |
| Priority: | medium | ||
| Version: | 3.4.0 | CC: | aos-bugs, jeder, jeharris, jmencak, jokerman, mmccomas, pdwyer, rbost |
| Target Milestone: | --- | ||
| Target Release: | --- | ||
| Hardware: | Unspecified | ||
| OS: | Unspecified | ||
| Whiteboard: | |||
| Fixed In Version: | Doc Type: | If docs needed, set a value | |
| Doc Text: | Story Points: | --- | |
| Clone Of: | Environment: | ||
| Last Closed: | 2017-01-24 05:13:20 UTC | Type: | Bug |
| Regression: | --- | Mount Type: | --- |
| Documentation: | --- | CRM: | |
| Verified Versions: | Category: | --- | |
| oVirt Team: | --- | RHEL 7.3 requirements from Atomic Host: | |
| Cloudforms Team: | --- | Target Upstream Version: | |
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Description
Vikram Goyal
2016-10-14 04:15:37 UTC
Linking a thread: http://post-office.corp.redhat.com/archives/atomic-networking/2016-October/msg00046.html Consensus seems to be net.ipv4.neigh.default.gc_thresh1 = 8192 net.ipv4.neigh.default.gc_thresh2 = 32768 net.ipv4.neigh.default.gc_thresh3 = 65536 are sane values to use when the default settings: net.ipv6.neigh.default.gc_thresh1 = 128 net.ipv6.neigh.default.gc_thresh2 = 512 net.ipv6.neigh.default.gc_thresh3 = 1024 begin to cause issues. Note that Documentation/networking/ip-sysctl.txt only mentions gc_thresh1 and gc_thresh3. Possibly a kernel component bug rather than a documentation one? We have a KCS (https://access.redhat.com/solutions/23454) which says "gc_thresh1 is not used anymore and is present for backwards compatibility". I'm unsure about that, as of d5f963fc3f "net/core/neighbour.c" line 766 is using gc_thresh1, line 280 using gc_thresh2. I propose the following text to be added to the documentation. As it is HAProxy specific, probably right behind "Preventing Connection Failures During Restarts"? == ARP cache tuning for large scale deployments In OCP deployments with large numbers of routes (greater than the value of ```net.ipv4.neigh.default.gc_thresh3```, which is 1024 by default), it is necessary to increase the default values of sysctl variables to allow more entries in the ARP cache. === Issue description In such large deployments the problem manifests itself by kernel messages similar to the following ones: ``` [ 1738.811139] net_ratelimit: 1045 callbacks suppressed [ 1743.823136] net_ratelimit: 293 callbacks suppressed ``` Also, when using the ```oc``` client the commands fail and the user receives the following messages: ``` Unable to connect to the server: dial tcp: lookup <hostname> on <ip>:<port>: write udp <ip>:<port>-><ip>:<port>: write: invalid argument ``` === Resolution To verify the actual amount of ARP entries for IPv4, you could run the following: ``` # ip -4 neigh show nud all | wc -l ``` If the number begins to approach the ```net.ipv4.neigh.default.gc_thresh3``` threshold, the following sysctl values are recommended for large scale deployments: ``` net.ipv4.neigh.default.gc_thresh1 = 8192 net.ipv4.neigh.default.gc_thresh2 = 32768 net.ipv4.neigh.default.gc_thresh3 = 65536 ``` To make these settings permanent across reboots it is advised to create a https://access.redhat.com/solutions/1305833[custom tuned profile]. Thanks, all. I've submitted a PR for this. Feel free to make any comments there or here: https://github.com/openshift/openshift-docs/pull/3242 Commit pushed to master at https://github.com/openshift/openshift-docs https://github.com/openshift/openshift-docs/commit/70602f79bb94648a911da30d0ec4ce6dd14ab070 Merge pull request #3242 from bfallonf/haproxy_1384746 Bug 1384746 added section on tuning sysctl values Link to released docs: https://access.redhat.com/documentation/en/openshift-container-platform/3.4/single/installation-and-configuration/#deploy-router-arp-cach-tuning-for-large-scale-clusters *** Bug 1566671 has been marked as a duplicate of this bug. *** |