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Signed-off-by: Miek Gieben <miek@miek.nl>
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Miek Gieben
2020-01-25 08:52:10 +01:00
parent 663f10c34d
commit 1812b5d73b
1 changed files with 12 additions and 11 deletions
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plugin/traffic/README.md
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@@ -6,13 +6,18 @@
## Description
The *traffic* plugin is a balancer that allows traffic steering, weighted responses
and draining of clusters. The cluster information is retrieved from a service
discovery manager that implements the service discovery protocols from Envoy
[implements](https://www.envoyproxy.io/docs/envoy/latest/api-docs/xds_protocol). It connects to the
manager using the Aggregated Discovery Service (ADS) protocol.
The *traffic* plugin is a balancer that allows traffic steering, weighted responses and draining of
clusters.
A Cluster in Envoy is defined as: "A group of logically similar endpoints that Envoy connects to."
The cluster information is retrieved from a service discovery manager that implements the service
discovery [protocols from Envoy implements](https://www.envoyproxy.io/docs/envoy/latest/api-docs/xds_protocol).
It connects to the manager using the Aggregated Discovery Service (ADS) protocol. Endpoints and
clusters are discovered every 10 seconds. The plugin hands out responses that adhere to these
assignments. Only endpoints that are *healthy* are handed out.
If *traffic*'s `locality` has been set the answers can be localized.
A cluster in Envoy is defined as: "A group of logically similar endpoints that Envoy connects to."
Each cluster has a name, which *traffic* extends to be a domain name. See "Naming Clusters" below.
The use case for this plugin is when a cluster has endpoints running in multiple (Kubernetes?)
@@ -20,10 +25,6 @@ clusters and you need to steer traffic to (or away) from these endpoints, i.e. e
be upgraded, so all traffic to it is drained. Or the entire Kubernetes needs to upgraded, and *all*
endpoints need to be drained from it.
*Traffic* discovers the endpoints via Envoy's xDS protocol (using ADS). Endpoints and clusters are
discovered every 10 seconds. The plugin hands out responses that adhere to these assignments. Only
endpoints that are *healthy* are handed out.
For A and AAAA queries each DNS response contains a single IP address that's considered the best
one. The TTL on these answer is set to 5s. It will only return successful responses either with an
answer or otherwise a NODATA response. Queries for non-existent clusters get a NXDOMAIN, where the
@@ -34,7 +35,7 @@ enough to select the best one. When SRV records are returned, the endpoint DNS n
`endpoint-<N>.<cluster>.<zone>` that carries the IP address. Querying for these synthesized names
works as well.
Load reporting is not supported for the following reason. A DNS query is done by a resolver.
Load reporting is not supported for the following reason: A DNS query is done by a resolver.
Behind this resolver (which can also cache) there may be many clients that will use this reply. The
responding server (CoreDNS) has no idea how many clients use this resolver. So reporting a load of
+1 on the CoreDNS side can results in anything from 1 to 1000+ of queries on the endpoint, making