fix: upon DNS refresh() failure use previous values (#17561)

DNS refresh() in-case of MinIO can safely re-use
the previous values on bare-metal setups, since
bare-metal arrangements do not change DNS in any 
manner commonly.

This PR simplifies that, we only ever need DNS caching
on bare-metal setups.

- On containerized setups do not enable DNS
  caching at all, as it may have adverse effects on
  the overall effectiveness of k8s DNS systems.

  k8s DNS systems are dynamic and expect applications
  to avoid managing DNS caching themselves, instead
  provide a cleaner container native caching
  implementations that must be used.

- update IsDocker() detection, including podman runtime

- move to minio/dnscache fork for a simpler package

internal/http/transports.go

@@ -21,13 +21,11 @@ import (
 	"context"
 	"crypto/tls"
 	"crypto/x509"
-	"net"
 	"net/http"
 	"syscall"
 	"time"
 
 	"github.com/minio/pkg/certs"
-	"github.com/rs/dnscache"
 )
 
 // tlsClientSessionCacheSize is the cache size for client sessions.
@@ -35,11 +33,8 @@ var tlsClientSessionCacheSize = 100
 
 // ConnSettings - contains connection settings.
 type ConnSettings struct {
-	// If this is non-nil, DNSCache and DialTimeout are ignored.
-	DialContext func(ctx context.Context, network, addr string) (net.Conn, error)
-
-	// Dial settings, used if DialContext is nil.
-	DNSCache    *dnscache.Resolver
+	DialContext DialContext // Custom dialContext, DialTimeout is ignored if this is already setup.
+	LookupHost  LookupHost  // Custom lookupHost, is nil on containerized deployments.
 	DialTimeout time.Duration
 
 	// TLS Settings
@@ -57,7 +52,7 @@ type ConnSettings struct {
 func (s ConnSettings) getDefaultTransport() *http.Transport {
 	dialContext := s.DialContext
 	if dialContext == nil {
-		dialContext = DialContextWithDNSCache(s.DNSCache, NewInternodeDialContext(s.DialTimeout, s.TCPOptions))
+		dialContext = DialContextWithLookupHost(s.LookupHost, NewInternodeDialContext(s.DialTimeout, s.TCPOptions))
 	}
 
 	tlsClientConfig := tls.Config{