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This should help improve load balancing when using TCP load balancers, where DNS will report a single IP and each connection made to that IP is pinned to a single backend instance.
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// Copyright 2023 Buf Technologies, Inc. | ||
// | ||
// Licensed under the Apache License, Version 2.0 (the "License"); | ||
// you may not use this file except in compliance with the License. | ||
// You may obtain a copy of the License at | ||
// | ||
// http://www.apache.org/licenses/LICENSE-2.0 | ||
// | ||
// Unless required by applicable law or agreed to in writing, software | ||
// distributed under the License is distributed on an "AS IS" BASIS, | ||
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. | ||
// See the License for the specific language governing permissions and | ||
// limitations under the License. | ||
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package resolver | ||
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import ( | ||
"context" | ||
"io" | ||
) | ||
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// MinConnections decorates the given resolver so it sends a set of addresses that has at | ||
// least as many entries as the given minimum. If the given resolver provides a smaller | ||
// set of addresses, it replicates those addresses until the give minimum is reached. | ||
// | ||
// This will cause a client to effectively make redundant connections to the same address | ||
// which is particularly useful when the addresses are virtual IPs, which actually have | ||
// multiple servers behind them. This is appropriate for environments like Kubernetes | ||
// (which uses virtual IPs for non-headless services) and for use with services that have | ||
// layer-4 (TCP) proxies/load balancers in front of them. | ||
// | ||
// To avoid "hot spotting", where one backend address gets more load than others, this | ||
// always fully replicates the set. So it will always report at least minAddresses, but | ||
// could report nearly twice as many: in the case where the set from the underlying | ||
// resolver has minAddresses-1 entries, this will provide (minAddresses-1)*2 entries. | ||
func MinConnections(other Resolver, minAddresses int) Resolver { | ||
return &minConnsResolver{res: other, min: minAddresses} | ||
} | ||
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type minConnsResolver struct { | ||
res Resolver | ||
min int | ||
} | ||
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func (m *minConnsResolver) New(ctx context.Context, scheme, hostPort string, receiver Receiver, refresh <-chan struct{}) io.Closer { | ||
return m.res.New(ctx, scheme, hostPort, &minConnsReceiver{rcvr: receiver, min: m.min}, refresh) | ||
} | ||
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type minConnsReceiver struct { | ||
rcvr Receiver | ||
min int | ||
} | ||
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func (m *minConnsReceiver) OnResolve(addresses []Address) { | ||
if len(addresses) >= m.min || len(addresses) == 0 { | ||
// Already enough addresses; OR zero addresses, in which case, no amount of replication can help. | ||
m.rcvr.OnResolve(addresses) | ||
return | ||
} | ||
multiplier := m.min / len(addresses) | ||
if len(addresses)*multiplier < m.min { | ||
multiplier++ // div rounded down | ||
} | ||
scaledAddrs := make([]Address, 0, len(addresses)*multiplier) | ||
for i := 0; i < multiplier; i++ { | ||
scaledAddrs = append(scaledAddrs, addresses...) | ||
} | ||
m.rcvr.OnResolve(scaledAddrs) | ||
} | ||
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func (m *minConnsReceiver) OnResolveError(err error) { | ||
m.rcvr.OnResolveError(err) | ||
} |
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// Copyright 2023 Buf Technologies, Inc. | ||
// | ||
// Licensed under the Apache License, Version 2.0 (the "License"); | ||
// you may not use this file except in compliance with the License. | ||
// You may obtain a copy of the License at | ||
// | ||
// http://www.apache.org/licenses/LICENSE-2.0 | ||
// | ||
// Unless required by applicable law or agreed to in writing, software | ||
// distributed under the License is distributed on an "AS IS" BASIS, | ||
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. | ||
// See the License for the specific language governing permissions and | ||
// limitations under the License. | ||
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package resolver_test | ||
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import ( | ||
"context" | ||
"testing" | ||
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. "github.com/bufbuild/httplb/resolver" | ||
"github.com/stretchr/testify/assert" | ||
) | ||
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func TestMinConnections(t *testing.T) { | ||
t.Parallel() | ||
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refreshCh := make(chan struct{}) | ||
defer close(refreshCh) | ||
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addrFoo := Address{HostPort: "foo"} | ||
addrBar := Address{HostPort: "bar"} | ||
addrBaz := Address{HostPort: "baz"} | ||
addrQux := Address{HostPort: "qux"} | ||
addresses := []Address{addrFoo, addrBar, addrBaz, addrQux} | ||
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var resolver fakeResolver | ||
minResolver := MinConnections(&resolver, 6) | ||
var receiver fakeReceiver | ||
_ = minResolver.New(context.Background(), "", "", &receiver, refreshCh) | ||
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resolver.receiver.OnResolve([]Address{}) | ||
assert.Equal(t, receiver.addrs, []Address{}) | ||
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resolver.receiver.OnResolve([]Address{addrFoo}) | ||
assert.Equal(t, receiver.addrs, []Address{ // single address, repeated 6 times | ||
addrFoo, addrFoo, addrFoo, addrFoo, addrFoo, addrFoo, | ||
}) | ||
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resolver.receiver.OnResolve([]Address{addrFoo, addrBar}) | ||
assert.Equal(t, receiver.addrs, []Address{ // both addresses, each repeated 3 times | ||
addrFoo, addrBar, addrFoo, addrBar, addrFoo, addrBar, | ||
}) | ||
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resolver.receiver.OnResolve(append([]Address{}, addresses...)) | ||
assert.Equal(t, receiver.addrs, []Address{ // all four addresses, each repeated | ||
addrFoo, addrBar, addrBaz, addrQux, addrFoo, addrBar, addrBaz, addrQux, | ||
}) | ||
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minResolver = MinConnections(&resolver, 3) | ||
_ = minResolver.New(context.Background(), "", "", &receiver, refreshCh) | ||
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resolver.receiver.OnResolve(append([]Address{}, addresses...)) | ||
assert.Equal(t, receiver.addrs, []Address{ // all four addresses, no repetition | ||
addrFoo, addrBar, addrBaz, addrQux, | ||
}) | ||
} |