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net/dnsfallback: disable recursive resolver for now 

It seems to be implicated in a CPU consumption bug that's not yet
understood. Disable it until we understand.

Updates tailscale/corp#15261

Change-Id: Ia6d0c310da6464dda79a70fc3c18be0782812d3f
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
This commit is contained in:
Brad Fitzpatrick 2023-10-16 09:30:47 -07:00 committed by Brad Fitzpatrick
parent 8a5b02133d
commit 95faefd1f6
1 changed files with 10 additions and 2 deletions
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12
net/dnsfallback/dnsfallback.go
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@ -39,14 +39,22 @@ import (
"tailscale.com/util/slicesx"
)
var disableRecursiveResolver = envknob.RegisterBool("TS_DNSFALLBACK_DISABLE_RECURSIVE_RESOLVER")
var (
optRecursiveResolver = envknob.RegisterOptBool("TS_DNSFALLBACK_RECURSIVE_RESOLVER")
disableRecursiveResolver = envknob.RegisterBool("TS_DNSFALLBACK_DISABLE_RECURSIVE_RESOLVER") // legacy pre-1.52 env knob name
)
// MakeLookupFunc creates a function that can be used to resolve hostnames
// (e.g. as a LookupIPFallback from dnscache.Resolver).
// The netMon parameter is optional; if non-nil it's used to do faster interface lookups.
func MakeLookupFunc(logf logger.Logf, netMon *netmon.Monitor) func(ctx context.Context, host string) ([]netip.Addr, error) {
return func(ctx context.Context, host string) ([]netip.Addr, error) {
if disableRecursiveResolver() {
// If they've explicitly disabled the recursive resolver with the legacy
// TS_DNSFALLBACK_DISABLE_RECURSIVE_RESOLVER envknob or not set the
// newer TS_DNSFALLBACK_RECURSIVE_RESOLVER to true, then don't use the
// recursive resolver. (tailscale/corp#15261) In the future, we might
// change the default (the opt.Bool being unset) to mean enabled.
if disableRecursiveResolver() || !optRecursiveResolver().EqualBool(true) {
return lookup(ctx, host, logf, netMon)
}