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Add more to the README

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Signed-off-by: Miek Gieben <miek@miek.nl>
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Miek Gieben
2020-01-11 08:48:30 +01:00
parent 3de4ab3c0b
commit 3e095ad847
3 changed files with 47 additions and 8 deletions
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Hacking on *traffic*
Repos used:
<https://github.com/envoyproxy/go-control-plane>
: implements control plane, has testing stuff in pkg/test/main (iirc).
<https://github.com/grpc/grpc-go/tree/master/xds/internal/client>
: implements client for xDS - can probably list all code out from there.
To see if things are working start the testing control plane from go-control-plane:

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plugin/traffic/README.md
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## Description ## Description
The *traffic* plugin is a load balancer that allows traffic steering, weighted responses and The *traffic* plugin is a load balancer that allows traffic steering, weighted responses and
draining of endpoints. It discovers the enpoints via the Envoy xDS protocol, specifically messages draining of endpoints. The use case for this plugin is when a service is running in multiple
of the type "envoy.api.v2.ClusterLoadAssignment", these contain endpoints and an (optional) weight (Kubernetes?) clusters and need to steer traffic to (or away) from these, i.e. cluster A needs to be
for each. The `cluster_name` or `service_name` for a service must be a domain name. upgraded, so all traffic to it is drained, while cluster B now takes on all the extra load. After
the maintenance cluster A is simply undrained.
The plugin takes care of handing out responses that adhere to these assignments. *Traffic* discovers the endpoints via the Envoy xDS protocol, specifically messages of the type
"envoy.api.v2.ClusterLoadAssignment", these contain endpoints and an (optional) weight for each.
The `cluster_name` or `service_name` for a service must be a domain name. (TODO: check is this is
already the case). The plugin hands out responses that adhere to these assignments.
Assignments will need to be updated frequently, as discussed the [Envoy xDS Assignments will need to be updated frequently, as discussed the [Envoy xDS
protocol](https://www.envoyproxy.io/docs/envoy/latest/api-docs/xds_protocol) documentation. Each protocol](https://www.envoyproxy.io/docs/envoy/latest/api-docs/xds_protocol) documentation.
response will contain one address record; which *traffic* considers the optimal one.
When there are no assignments for a service name (yet), the responses will also be modified (see Multiple endpoints for a service may exist; for every query *traffic* will hand out exactly one
below). address. When there are no assignments for a service name (yet), the responses will also be modified
(see below).
*Traffic* will load balance A and AAAA queries. As said, it will return precisely one record in a *Traffic* will load balance A and AAAA queries. As said, it will return precisely one record in a
response. If a service should be load balanced, but no assignment can be found a random record from response. If a service should be load balanced, but no assignment can be found a random record from
@@ -30,6 +34,8 @@ The *traffic* plugin has no notion of draining, drop overload and anything that
acts upon assignments*. This is means that if a endpoint goes down and *traffic* has not seen a new acts upon assignments*. This is means that if a endpoint goes down and *traffic* has not seen a new
assignment yet, it will still include this endpoint address in responses. assignment yet, it will still include this endpoint address in responses.
Findign the xDS endpoint.
## Syntax ## Syntax
~~~ ~~~
@@ -74,6 +80,13 @@ Authority section will be removed.
If no assignment, randomly pick an address If no assignment, randomly pick an address
other types then A and AAAA, like SRV - do the same selection. other types then A and AAAA, like SRV - do the same selection.
## Limitations
Loadreporting via xDS is not supported; this can be implemented, but there are some things that make
this difficult. A single (DNS) query is done by a resolver. Behind this resolver there may be many
clients that will use this assignment.
## Bugs ## Bugs
This plugin does not play nice with DNSSEC - if the endpoint returns signatures with the answer; they This plugin does not play nice with DNSSEC - if the endpoint returns signatures with the answer; they
@@ -85,3 +98,8 @@ will be stripped. You can optionally sign responses on the fly by using the *dns
* https://blog.christianposta.com/envoy/guidance-for-building-a-control-plane-to-manage-envoy-proxy-based-infrastructure/ * https://blog.christianposta.com/envoy/guidance-for-building-a-control-plane-to-manage-envoy-proxy-based-infrastructure/
* https://github.com/envoyproxy/envoy/blob/442f9fcf21a5f091cec3fe9913ff309e02288659/api/envoy/api/v2/discovery.proto#L63 * https://github.com/envoyproxy/envoy/blob/442f9fcf21a5f091cec3fe9913ff309e02288659/api/envoy/api/v2/discovery.proto#L63
* This is a [post on weighted random selection](https://medium.com/@peterkellyonline/weighted-random-selection-3ff222917eb6). * This is a [post on weighted random selection](https://medium.com/@peterkellyonline/weighted-random-selection-3ff222917eb6).
# TODO
* wording: cluster, endpoints, assignments, service_name are all used and roughly mean the same
thing; unify this.

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This code is copied from
[https://github.com/grpc/grpc-go/tree/master/xds](https://github.com/grpc/grpc-go/tree/master/xds).
Grpc-go is also a consumer of the Envoy xDS data and acts upon it.
The *traffic* plugin only cares about clusters and endpoints, the following bits are deleted:
* lDS; listener discovery is not used here.
* rDS: routes have no use for DNS responses.
Load reporting is also not implemented, although this can be done on the DNS level.