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grpclb work

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Signed-off-by: Miek Gieben <miek@miek.nl>
This commit is contained in:
Miek Gieben
2020-03-04 11:55:42 +01:00
parent 5cce32db15
commit f72ecc7423
2 changed files with 91 additions and 15 deletions
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55
plugin/traffic/README.md
View File

@@ -35,15 +35,12 @@ 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.
[gRPC Service Config](https://github.com/grpc/proposal/blob/master/A2-service-configs-in-dns.md),
when queried for `_grpc_config.<cluster> TXT` such config will be returned. Currently the config
itself is staticly defined from the properties given in the *traffic* plugin itself.
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
the load reporting from *traffic* highly inaccurate.
[gRPC LB SRV records](https://github.com/grpc/proposal/blob/master/A5-grpclb-in-dns.md) are
supported and returned by the *traffic* plugin. These are SRV records for
`_grpclb._tcp.<name>.<domain>` and point to the xDS management servers as used in the configuration.
The target name used for these SRV records is `grpclb-<N>.<domain>`. This means a cluster names
of `grpclb-N` are illegal, because it used by *traffic* itself. See "Naming Clusters" below for
details.
*Traffic* implements version 3 of the xDS API. It works with the management server as written in
<https://github.com/miekg/xds>.
@@ -63,7 +60,7 @@ The extended syntax is available if you want more control.
~~~
traffic TO... {
node ID
id ID
locality REGION[,ZONE[,SUBZONE]] [REGION[,ZONE[,SUBZONE]]]...
tls CERT KEY CA
tls_servername NAME
@@ -71,7 +68,7 @@ traffic TO... {
}
~~~
* `node` **ID** is how *traffic* identifies itself to the control plane. This defaults to
* `id` **ID** is how *traffic* identifies itself to the control plane. This defaults to
`coredns`.
* `locality` has a list of **REGION,ZONE,SUBZONE** sets. These tell *traffic* where its running
@@ -111,6 +108,16 @@ domain names. For example if the Server Block specifies `lb.example.org` as one
and "cluster-v0" is one of the load balanced cluster, *traffic* will respond to query asking for
`cluster-v0.lb.example.org.` and the same goes for `web`; `web.lb.example.org`.
For SRV queries all endpoints are returned, the SRV target names are synthesized:
`endpoint-<N>.web.lb.example.org` to take the example from above. *N* is an integer starting with 0.
gRPC LB integration is also done by returning the correct SRV records. A gRPC client will ask for
`_grpclb._tcp.web.lb.example.org` and expect to get the SRV (and address records) to tell it where
the gRPC LBs are. For each **TO** in the configuration *traffic* will return a SRV record. The
target name in the SRV are synthesized as well, using `grpclb-N` to prefix the zone from the Corefile,
i.e. `grpclb-0.lb.example.org` will be the gRPC name when using `lb.example.org` in the configuration.
Each `grpclb-N` target will have one address record, namely the one specified in the configuration.
## Localized Endpoints
Endpoints can be grouped by location, this location information is used if the `locality` property
@@ -153,7 +160,7 @@ established to the control plane.
~~~
lb.example.org {
traffic grpc://127.0.0.1:18000 {
node test-id
id test-id
}
debug
log
@@ -161,13 +168,35 @@ lb.example.org {
~~~
This will load balance any names under `lb.example.org` using the data from the manager running on
localhost on port 18000. The node ID will be `test-id` and no TLS will be used.
localhost on port 18000. The node ID will be `test-id` and no TLS will be used. Assuming a
management server returns config for `web` cluster, you can query CoreDNS for it, below we do an
address lookup, which returns an address for the endpoint. The second example shows a SRV lookup
which returns all endpoints.
~~~ sh
$ dig @localhost web.lb.example.org +noall +answer
web.lb.example.org. 5 IN A 127.0.1.1
$ dig @localhost web.lb.example.org SRV +noall +answer +additional
web.lb.example.org. 5 IN SRV 100 100 18008 endpoint-0.web.lb.example.org.
web.lb.example.org. 5 IN SRV 100 100 18008 endpoint-1.web.lb.example.org.
web.lb.example.org. 5 IN SRV 100 100 18008 endpoint-2.web.lb.example.org.
endpoint-0.web.lb.example.org. 5 IN A 127.0.1.1
endpoint-1.web.lb.example.org. 5 IN A 127.0.1.2
endpoint-2.web.lb.example.org. 5 IN A 127.0.2.1
~~~
## Bugs
Priority and locality information from ClusterLoadAssignments is not used. Multiple **TO** addresses
is not implemented. Credentials are not implemented.
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
the load reporting from *traffic* highly inaccurate.
## Also See
A Envoy management server and command line interface can be found on

51
plugin/traffic/traffic.go
View File

@@ -4,6 +4,7 @@ import (
"context"
"crypto/tls"
"fmt"
"net"
"strconv"
"strings"
"time"
@@ -28,6 +29,9 @@ type Traffic struct {
origins []string
loc []xds.Locality
grpcSRV []dns.RR // SRV records for grpc LB
grpcAddr []dns.RR // Address records for each LB (taken from **TOO**)
Next plugin.Handler
}
@@ -173,6 +177,9 @@ func (t *Traffic) serveEndpoint(ctx context.Context, state request.Request, endp
return 0, nil
}
// Name implements the plugin.Handler interface.
func (t *Traffic) Name() string { return "traffic" }
// soa returns a synthetic so for this zone.
func soa(z string) []dns.RR {
return []dns.RR{&dns.SOA{
@@ -187,5 +194,45 @@ func soa(z string) []dns.RR {
}}
}
// Name implements the plugin.Handler interface.
func (t *Traffic) Name() string { return "traffic" }
// srv record for grpclb endpoint.
func srv(i int, host, zone string) *dns.SRV {
target := fmt.Sprintf("grpclb-%d.%s", i, zone)
hdr := dns.RR_Header{Name: dnsutil.Join("_grpclb._tcp", zone), Class: dns.ClassINET, Rrtype: dns.TypeSRV}
_, p, _ := net.SplitHostPort(host) // err ignored already checked in setup
port, _ := strconv.Atoi(p)
return &dns.SRV{
Hdr: hdr,
// prio, weight -> 0
Port: uint16(port),
Target: target,
}
}
func a(i int, host, zone string) *dns.A {
owner := fmt.Sprintf("grpclb-%d.%s", i, zone)
hdr := dns.RR_Header{Name: owner, Class: dns.ClassINET, Rrtype: dns.TypeA}
h, _, _ := net.SplitHostPort(host)
ip := net.ParseIP(h)
if ip == nil {
return nil
}
if ip.To4() == nil {
return nil
}
return &dns.A{Hdr: hdr, A: ip.To4()}
}
func aaaa(i int, host, zone string) *dns.AAAA {
owner := fmt.Sprintf("grpclb-%d.%s", i, zone)
hdr := dns.RR_Header{Name: owner, Class: dns.ClassINET, Rrtype: dns.TypeAAAA}
h, _, _ := net.SplitHostPort(host)
ip := net.ParseIP(h)
if ip == nil {
return nil
}
if ip.To4() != nil {
return nil
}
return &dns.AAAA{Hdr: hdr, AAAA: ip.To16()}
}