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Implement SRV records

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Signed-off-by: Miek Gieben <miek@miek.nl>
This commit is contained in:
Miek Gieben
2020-01-18 20:12:25 +01:00
parent 63d3dfb0e1
commit 9d912fe2ca
5 changed files with 89 additions and 29 deletions
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14
plugin/traffic/README.md
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@@ -24,10 +24,13 @@ endpoints need to be drained from it.
discovered every 10 seconds. The plugin hands out responses that adhere to these assignments. Only
endpoints that are *healthy* are handed out.
Each DNS response contains a single IP address that's considered the best one. *Traffic* will load
balance A and AAAA queries. 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 minimal TTL is also set to 5s.
Each DNS response contains a single IP address (or SRV record) that's considered the best one.
*Traffic* will load balance A, AAAA and SRV queries. 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 minimal TTL is also set to 5s.
When an SRV record is returned an endpoint DNS name is synthesized `endpoint-0.<cluster>.<zone>` that
carries the IP address. Querying for these synthesized names works as well.
The *traffic* plugin has no notion of draining, drop overload and anything that advanced, *it just
acts upon assignments*. This is means that if a endpoint goes down and *traffic* has not seen a new
@@ -37,7 +40,7 @@ Load reporting is not supported for the following reason. A DNS query is done by
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 *trafifc* highly inaccurate.
the load reporting from *traffic* highly inaccurate.
## Syntax
@@ -97,7 +100,6 @@ If monitoring is enabled (via the *prometheus* plugin) then the following metric
* `coredns_traffic_clusters_tracked{}` the number of tracked clusters.
## Examples
~~~

28
plugin/traffic/traffic.go
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@@ -38,13 +38,28 @@ func (t *Traffic) ServeDNS(ctx context.Context, w dns.ResponseWriter, r *dns.Msg
m.SetReply(r)
m.Authoritative = true
addr, ok := t.c.Select(cluster)
addr, port, ok := t.c.Select(cluster)
if !ok {
// ok the cluster (which has potentially extra labels), doesn't exist, but we may have a query for endpoint-0.<cluster>.
// check if we have 2 labels and that the first equals endpoint-0.
if dns.CountLabel(cluster) != 2 {
m.Ns = soa(state.Zone)
m.Rcode = dns.RcodeNameError
w.WriteMsg(m)
return 0, nil
}
labels := dns.SplitDomainName(cluster)
if strings.Compare(labels[0], "endpoint-0") == 0 {
// recheck if the cluster exist.
addr, port, ok = t.c.Select(labels[1])
if !ok {
m.Ns = soa(state.Zone)
m.Rcode = dns.RcodeNameError
w.WriteMsg(m)
return 0, nil
}
}
}
if addr == nil {
log.Debugf("No (healthy) endpoints found for %q", cluster)
@@ -66,7 +81,16 @@ func (t *Traffic) ServeDNS(ctx context.Context, w dns.ResponseWriter, r *dns.Msg
m.Ns = soa(state.Zone)
break
}
m.Answer = []dns.RR{&dns.AAAA{Hdr: dns.RR_Header{Name: state.QName(), Rrtype: dns.TypeA, Class: dns.ClassINET, Ttl: 5}, AAAA: addr}}
m.Answer = []dns.RR{&dns.AAAA{Hdr: dns.RR_Header{Name: state.QName(), Rrtype: dns.TypeAAAA, Class: dns.ClassINET, Ttl: 5}, AAAA: addr}}
case dns.TypeSRV:
target := dnsutil.Join("endpoint-0", cluster) + state.Zone
m.Answer = []dns.RR{&dns.SRV{Hdr: dns.RR_Header{Name: state.QName(), Rrtype: dns.TypeA, Class: dns.ClassINET, Ttl: 5},
Priority: 100, Weight: 100, Port: port, Target: target}}
if addr.To4() == nil {
m.Extra = []dns.RR{&dns.AAAA{Hdr: dns.RR_Header{Name: target, Rrtype: dns.TypeA, Class: dns.ClassINET, Ttl: 5}, AAAA: addr}}
} else {
m.Extra = []dns.RR{&dns.A{Hdr: dns.RR_Header{Name: target, Rrtype: dns.TypeA, Class: dns.ClassINET, Ttl: 5}, A: addr}}
}
default:
m.Ns = soa(state.Zone)
}

43
plugin/traffic/traffic_test.go
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@@ -47,15 +47,22 @@ func TestTraffic(t *testing.T) {
{
cla: &xdspb.ClusterLoadAssignment{
ClusterName: "web",
Endpoints: endpoints([]EndpointHealth{{"127.0.0.1", corepb.HealthStatus_HEALTHY}}),
Endpoints: endpoints([]EndpointHealth{{"127.0.0.1", 18008, corepb.HealthStatus_HEALTHY}}),
},
cluster: "web", qtype: dns.TypeA, rcode: dns.RcodeSuccess, answer: "127.0.0.1",
},
{
cla: &xdspb.ClusterLoadAssignment{
ClusterName: "web",
Endpoints: endpoints([]EndpointHealth{{"::1", 18008, corepb.HealthStatus_HEALTHY}}),
},
cluster: "web", qtype: dns.TypeAAAA, rcode: dns.RcodeSuccess, answer: "::1",
},
// unknown backend
{
cla: &xdspb.ClusterLoadAssignment{
ClusterName: "web",
Endpoints: endpoints([]EndpointHealth{{"127.0.0.1", corepb.HealthStatus_UNKNOWN}}),
Endpoints: endpoints([]EndpointHealth{{"127.0.0.1", 18008, corepb.HealthStatus_UNKNOWN}}),
},
cluster: "web", qtype: dns.TypeA, rcode: dns.RcodeSuccess, ns: true,
},
@@ -64,12 +71,32 @@ func TestTraffic(t *testing.T) {
cla: &xdspb.ClusterLoadAssignment{
ClusterName: "web",
Endpoints: endpoints([]EndpointHealth{
{"127.0.0.1", corepb.HealthStatus_UNKNOWN},
{"127.0.0.2", corepb.HealthStatus_HEALTHY},
{"127.0.0.1", 18008, corepb.HealthStatus_UNKNOWN},
{"127.0.0.2", 18008, corepb.HealthStatus_HEALTHY},
}),
},
cluster: "web", qtype: dns.TypeA, rcode: dns.RcodeSuccess, answer: "127.0.0.2",
},
// SRV query healthy backend
{
cla: &xdspb.ClusterLoadAssignment{
ClusterName: "web",
Endpoints: endpoints([]EndpointHealth{
{"127.0.0.2", 18008, corepb.HealthStatus_HEALTHY},
}),
},
cluster: "web", qtype: dns.TypeSRV, rcode: dns.RcodeSuccess, answer: "endpoint-0.web.lb.example.org.",
},
// A query for endpoint-0.
{
cla: &xdspb.ClusterLoadAssignment{
ClusterName: "web",
Endpoints: endpoints([]EndpointHealth{
{"127.0.0.2", 18008, corepb.HealthStatus_HEALTHY},
}),
},
cluster: "endpoint-0.web", qtype: dns.TypeA, rcode: dns.RcodeSuccess, answer: "127.0.0.2",
},
}
ctx := context.TODO()
@@ -105,18 +132,19 @@ func TestTraffic(t *testing.T) {
addr = x.A.String()
case *dns.AAAA:
addr = x.AAAA.String()
case *dns.SRV:
addr = x.Target
}
if tc.answer != addr {
t.Errorf("Test %d: Expected answer %s, but got %s", i, tc.answer, addr)
}
}
}
}
type EndpointHealth struct {
Address string
Port uint16
Health corepb.HealthStatus
}
@@ -131,6 +159,9 @@ func endpoints(e []EndpointHealth) []*endpointpb.LocalityLbEndpoints {
Address: &corepb.Address_SocketAddress{
SocketAddress: &corepb.SocketAddress{
Address: e[i].Address,
PortSpecifier: &corepb.SocketAddress_PortValue{
PortValue: uint32(e[i].Port),
},
},
},
},

21
plugin/traffic/xds/assignment.go
View File

@@ -59,12 +59,11 @@ func (a *assignment) clusters() []string {
return clusters
}
// Select selects a backend from cluster load assignments, using weighted random selection. It only selects
// backends that are reporting healthy.
func (a *assignment) Select(cluster string) (net.IP, bool) {
// Select selects a backend from cluster load assignments, using weighted random selection. It only selects backends that are reporting healthy.
func (a *assignment) Select(cluster string) (ip net.IP, port uint16, exists bool) {
cla := a.ClusterLoadAssignment(cluster)
if cla == nil {
return nil, false
return nil, 0, false
}
total := 0
@@ -79,7 +78,7 @@ func (a *assignment) Select(cluster string) (net.IP, bool) {
}
}
if healthy == 0 {
return nil, true
return nil, 0, true
}
if total == 0 {
@@ -92,12 +91,14 @@ func (a *assignment) Select(cluster string) (net.IP, bool) {
continue
}
if r == i {
return net.ParseIP(lb.GetEndpoint().GetAddress().GetSocketAddress().GetAddress()), true
addr := net.ParseIP(lb.GetEndpoint().GetAddress().GetSocketAddress().GetAddress())
port := uint16(lb.GetEndpoint().GetAddress().GetSocketAddress().GetPortValue())
return addr, port, true
}
i++
}
}
return nil, true
return nil, 0, true
}
r := rand.Intn(total) + 1
@@ -108,9 +109,11 @@ func (a *assignment) Select(cluster string) (net.IP, bool) {
}
r -= int(lb.GetLoadBalancingWeight().GetValue())
if r <= 0 {
return net.ParseIP(lb.GetEndpoint().GetAddress().GetSocketAddress().GetAddress()), true
addr := net.ParseIP(lb.GetEndpoint().GetAddress().GetSocketAddress().GetAddress())
port := uint16(lb.GetEndpoint().GetAddress().GetSocketAddress().GetPortValue())
return addr, port, true
}
}
}
return nil, true
return nil, 0, true
}

4
plugin/traffic/xds/client.go
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@@ -228,9 +228,9 @@ func (c *Client) receive(stream adsStream) error {
// Select returns an address that is deemed to be the correct one for this cluster. The returned
// boolean indicates if the cluster exists.
func (c *Client) Select(cluster string) (net.IP, bool) {
func (c *Client) Select(cluster string) (net.IP, uint16, bool) {
if cluster == "" {
return nil, false
return nil, 0, false
}
return c.assignments.Select(cluster)
}