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Add max upstream connections dns-proxy option (#290)

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* Add max upstream connections dns-proxy option

Allows defining a limit to the number of connections that can be
established with the upstream DNS host.

If left unset, there may be situations where connections fail to
establish, which causes the Transport to create an influx of connections
causing upstream to throttle our requests and triggering a runaway
effect resulting in high CPU usage. See https://github.com/cloudflare/cloudflared/issues/91

* Code review with proposed changes

* Add max upstream connections flag to tunnel flags

* Reduce DNS proxy max upstream connections default value

Reduce the default value of maximum upstream connections on the DNS
proxy to guarantee it works on single-core and other low-end hardware.
Further testing could allow for a safe increase of this value.

* Update dns-proxy flag name

Also remove `MaxUpstreamConnsFlag` const as it's no longer referenced in more than one place and to make things more consistent with how the other flags are referenced.

Co-authored-by: Adam Chalmers <achalmers@cloudflare.com>
This commit is contained in:
David Jimenez
2021-02-12 17:32:29 +00:00
committed by GitHub
parent e7354f4768
commit d7c4a89106
6 changed files with 54 additions and 17 deletions
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17
tunneldns/tunnel.go
View File

@@ -21,8 +21,9 @@ import (
)
const (
LogFieldAddress = "address"
LogFieldURL = "url"
LogFieldAddress = "address"
LogFieldURL = "url"
MaxUpstreamConnsDefault = 5
)
// Listener is an adapter between CoreDNS server and Warp runnable
@@ -69,6 +70,12 @@ func Command(hidden bool) *cli.Command {
Value: cli.NewStringSlice("https://162.159.36.1/dns-query", "https://162.159.46.1/dns-query", "https://[2606:4700:4700::1111]/dns-query", "https://[2606:4700:4700::1001]/dns-query"),
EnvVars: []string{"TUNNEL_DNS_BOOTSTRAP"},
},
&cli.IntFlag{
Name: "max-upstream-conns",
Usage: "Maximum concurrent connections to upstream. Setting to 0 means unlimited.",
Value: MaxUpstreamConnsDefault,
EnvVars: []string{"TUNNEL_DNS_MAX_UPSTREAM_CONNS"},
},
},
ArgsUsage: " ", // can't be the empty string or we get the default output
Hidden: hidden,
@@ -92,8 +99,10 @@ func Run(c *cli.Context) error {
uint16(c.Int("port")),
c.StringSlice("upstream"),
c.StringSlice("bootstrap"),
c.Int("max-upstream-conns"),
log,
)
if err != nil {
log.Err(err).Msg("Failed to create the listeners")
return err
@@ -175,12 +184,12 @@ func (l *Listener) Stop() error {
}
// CreateListener configures the server and bound sockets
func CreateListener(address string, port uint16, upstreams []string, bootstraps []string, log *zerolog.Logger) (*Listener, error) {
func CreateListener(address string, port uint16, upstreams []string, bootstraps []string, maxUpstreamConnections int, log *zerolog.Logger) (*Listener, error) {
// Build the list of upstreams
upstreamList := make([]Upstream, 0)
for _, url := range upstreams {
log.Info().Str(LogFieldURL, url).Msg("Adding DNS upstream")
upstream, err := NewUpstreamHTTPS(url, bootstraps, log)
upstream, err := NewUpstreamHTTPS(url, bootstraps, maxUpstreamConnections, log)
if err != nil {
return nil, errors.Wrap(err, "failed to create HTTPS upstream")
}