network related refactor

Signed-off-by: Alex Suraci <alex@dagger.io>

cmd/shim/main.go

@@ -23,6 +23,7 @@ import (
 	"github.com/cenkalti/backoff/v4"
 	"github.com/dagger/dagger/core"
 	"github.com/dagger/dagger/engine"
+	"github.com/dagger/dagger/network"
 	"github.com/dagger/dagger/router"
 	"github.com/google/uuid"
 	"github.com/opencontainers/runtime-spec/specs-go"
@@ -697,7 +698,7 @@ func collectSearchDomains(resolv string) ([]string, error) {
 
 		domains := strings.Fields(srcScan.Text())[1:]
 		for _, domain := range domains {
-			if strings.HasSuffix(domain, ".dagger.local") {
+			if strings.HasSuffix(domain, network.DomainSuffix) {
 				daggerDomains = append(daggerDomains, domain)
 			}
 		}

core/service.go

@@ -11,6 +11,7 @@ import (
 	"time"
 
 	"github.com/dagger/dagger/core/pipeline"
+	"github.com/dagger/dagger/network"
 	"github.com/dagger/dagger/router"
 	"github.com/moby/buildkit/client/llb"
 	bkgw "github.com/moby/buildkit/frontend/gateway/client"
@@ -29,11 +30,15 @@ const DaggerNetwork = "dagger"
 var servicesDomain string
 var servicesDomainOnce = &sync.Once{}
 
-// ServicesDomain is a session-global domain suffix appended to every service's
+// SessionDomain is a session-global domain suffix appended to every service's
 // hostname. It is randomly generated on the first call.
-func ServicesDomain() string {
+//
+// Ideally we would base this on the Buildkit gateway session ID instead of
+// using global state, but for exporting we actually establish multiple gateway
+// sessions.
+func SessionDomain() string {
 	servicesDomainOnce.Do(func() {
-		servicesDomain = hostHashStr(identity.NewID()) + ".dagger.local"
+		servicesDomain = hostHashStr(identity.NewID()) + network.DomainSuffix
 	})
 	return servicesDomain
 }
@@ -377,7 +382,7 @@ func (svc *Service) Start(ctx context.Context, gw bkgw.Client, progSock *Socket)
 
 	vtx := rec.Vertex(dig, "start "+strings.Join(args, " "))
 
-	fullHost := host + "." + ServicesDomain()
+	fullHost := host + "." + SessionDomain()
 
 	health := newHealth(gw, fullHost, svc.Container.Ports)
 

engine/engine.go

@@ -188,7 +188,7 @@ func Start(ctx context.Context, startOpts Config, fn StartCallback) error {
 					return &networks.Config{
 						Dns: &networks.DNSConfig{
 							SearchDomains: append(
-								[]string{core.ServicesDomain()},
+								[]string{core.SessionDomain()},
 								startOpts.ExtraSearchDomains...,
 							),
 						},

network/consts.go

@@ -0,0 +1,7 @@
+package network
+
+// DomainSuffix is an extra domain suffix appended to every session's unique
+// domain. It is used to identify which domains to propagate from a parent
+// session's /etc/resolv.conf to a child (nested Dagger) session's network
+// config so that nested code can reach services in the parent.
+const DomainSuffix = ".dagger.local"