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Make sure user understands Outlier Detection is req'd for locality LB (#4854) 

* Make sure user understands Outlier Detection is req'd for locality LB

* Code review comments

* Fix lint issue

* code review
This commit is contained in:
Eric Van Norman 2019-08-29 09:25:32 -05:00 committed by Istio Automation
parent dbda0caef4
commit 118eb9c1fe
1 changed files with 8 additions and 3 deletions
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content/en/docs/ops/traffic-management/locality-load-balancing/index.md
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@ -35,6 +35,9 @@ As a result, this field does not need to be configured.
In order for Istio to determine locality, a Service must be associated with the caller.
To determine when instances are unhealthy, the proxies require an [outlier detection](/docs/reference/config/networking/v1alpha3/destination-rule/#OutlierDetection)
configuration in a destination rule for each service.
## Locality-prioritized load balancing
_Locality-prioritized load balancing_ is the default behavior for _locality load balancing_.
@ -44,6 +47,11 @@ remains within the same locality. When instances become unhealthy, traffic spill
instances in the next prioritized locality. This behavior continues until all localities are
receiving traffic. You can find the exact percentages in the [Envoy documentation](https://www.envoyproxy.io/docs/envoy/latest/intro/arch_overview/upstream/load_balancing/priority).
{{< warning >}}
If no outlier detection configurations are defined in destination rules, the proxy can't determine if an instance is healthy, and it
routes traffic globally even if you enabled **locality-prioritized** load balancing.
{{< /warning >}}
A typical prioritization for an Envoy with a locality of `us-west/zone2` is as follows:
- Priority 0: `us-west/zone2`
@ -58,9 +66,6 @@ The hierarchy of prioritization matches in the following order:
Proxies in the same zone but different regions are not considered local to one another.
In order for Envoy to determine when instances are unhealthy, an [Outlier Detection](/docs/reference/config/networking/v1alpha3/destination-rule/#OutlierDetection)
rule must be defined for each service.
### Overriding the Locality Fail-over
Sometimes, you need to constrain the traffic fail-over to avoid sending traffic to