updater: refactoring and set DNS server correctly

- Fix CLI operation not setting DNS server
- Fix periodic operation not setting DNS server
- Set DNS address for resolution once at start for both CLI and periodic operation
- Inject resolver to each provider instead of creating it within
- Use resolver settings on every call to `.Resolve` method, instead of passing it to constructor
- Move out minServers check from resolver

internal/provider/cyberghost/updater/resolve.go

@@ -6,7 +6,7 @@ import (
 	"github.com/qdm12/gluetun/internal/updater/resolver"
 )
 
-func newParallelResolver() (parallelResolver *resolver.Parallel) {
+func parallelResolverSettings(hosts []string) (settings resolver.ParallelSettings) {
 	const (
 		maxFailRatio    = 1
 		maxDuration     = 20 * time.Second
@@ -14,7 +14,8 @@ func newParallelResolver() (parallelResolver *resolver.Parallel) {
 		maxNoNew        = 4
 		maxFails        = 10
 	)
-	settings := resolver.ParallelSettings{
+	return resolver.ParallelSettings{
+		Hosts:        hosts,
 		MaxFailRatio: maxFailRatio,
 		Repeat: resolver.RepeatSettings{
 			MaxDuration:     maxDuration,
@@ -24,5 +25,4 @@ func newParallelResolver() (parallelResolver *resolver.Parallel) {
 			SortIPs:         true,
 		},
 	}
-	return resolver.NewParallelResolver(settings)
 }

internal/provider/cyberghost/updater/servers.go

@@ -4,9 +4,11 @@ package updater
 
 import (
 	"context"
+	"fmt"
 	"sort"
 
 	"github.com/qdm12/gluetun/internal/models"
+	"github.com/qdm12/gluetun/internal/provider/common"
 )
 
 func (u *Updater) FetchServers(ctx context.Context, minServers int) (
@@ -14,11 +16,17 @@ func (u *Updater) FetchServers(ctx context.Context, minServers int) (
 	possibleServers := getPossibleServers()
 
 	possibleHosts := possibleServers.hostsSlice()
-	hostToIPs, _, err := u.presolver.Resolve(ctx, possibleHosts, minServers)
+	resolveSettings := parallelResolverSettings(possibleHosts)
+	hostToIPs, _, err := u.presolver.Resolve(ctx, resolveSettings)
 	if err != nil {
 		return nil, err
 	}
 
+	if len(hostToIPs) < minServers {
+		return nil, fmt.Errorf("%w: %d and expected at least %d",
+			common.ErrNotEnoughServers, len(servers), minServers)
+	}
+
 	possibleServers.adaptWithIPs(hostToIPs)
 
 	servers = possibleServers.toSlice()

internal/provider/cyberghost/updater/updater.go

@@ -8,8 +8,8 @@ type Updater struct {
 	presolver common.ParallelResolver
 }
 
-func New() *Updater {
+func New(parallelResolver common.ParallelResolver) *Updater {
 	return &Updater{
-		presolver: newParallelResolver(),
+		presolver: parallelResolver,
 	}
 }