diff --git a/cluster/admitomatic/BUILD.bazel b/cluster/admitomatic/BUILD.bazel
index 5cb23ab..55c7466 100644
--- a/cluster/admitomatic/BUILD.bazel
+++ b/cluster/admitomatic/BUILD.bazel
@@ -5,13 +5,18 @@
     srcs = [
         "ingress.go",
         "main.go",
+        "service.go",
     ],
     importpath = "code.hackerspace.pl/hscloud/cluster/admitomatic",
     visibility = ["//visibility:private"],
     deps = [
+        "//cluster/admitomatic/config:go_default_library",
         "//go/mirko:go_default_library",
         "@com_github_golang_glog//:go_default_library",
         "@io_k8s_api//admission/v1beta1:go_default_library",
+        "@io_k8s_api//networking/v1beta1:go_default_library",
+        "@io_k8s_apimachinery//pkg/apis/meta/v1:go_default_library",
+        "@org_golang_google_protobuf//encoding/prototext:go_default_library",
     ],
 )
 
@@ -25,4 +30,10 @@
     name = "go_default_test",
     srcs = ["ingress_test.go"],
     embed = [":go_default_library"],
+    deps = [
+        "@io_k8s_api//admission/v1beta1:go_default_library",
+        "@io_k8s_api//networking/v1beta1:go_default_library",
+        "@io_k8s_apimachinery//pkg/apis/meta/v1:go_default_library",
+        "@io_k8s_apimachinery//pkg/runtime:go_default_library",
+    ],
 )
diff --git a/cluster/admitomatic/config/BUILD.bazel b/cluster/admitomatic/config/BUILD.bazel
new file mode 100644
index 0000000..0344526
--- /dev/null
+++ b/cluster/admitomatic/config/BUILD.bazel
@@ -0,0 +1,23 @@
+load("@rules_proto//proto:defs.bzl", "proto_library")
+load("@io_bazel_rules_go//go:def.bzl", "go_library")
+load("@io_bazel_rules_go//proto:def.bzl", "go_proto_library")
+
+proto_library(
+    name = "config_proto",
+    srcs = ["config.proto"],
+    visibility = ["//visibility:public"],
+)
+
+go_proto_library(
+    name = "config_go_proto",
+    importpath = "code.hackerspace.pl/hscloud/cluster/admitomatic/config",
+    proto = ":config_proto",
+    visibility = ["//visibility:public"],
+)
+
+go_library(
+    name = "go_default_library",
+    embed = [":config_go_proto"],
+    importpath = "code.hackerspace.pl/hscloud/cluster/admitomatic/config",
+    visibility = ["//visibility:public"],
+)
diff --git a/cluster/admitomatic/config/config.proto b/cluster/admitomatic/config/config.proto
new file mode 100644
index 0000000..460c571
--- /dev/null
+++ b/cluster/admitomatic/config/config.proto
@@ -0,0 +1,37 @@
+syntax = "proto3";
+package config;
+option go_package = "code.hackerspace.pl/hscloud/cluster/admitomatic/config";
+
+// Admitomatic configuration, passed as a text proto, for
+// example:
+//
+//  $ cat sample.pb.text
+//  allow_domain { namespace: "example" dns: "*.example.com" }
+//  allow_domain {
+//    namespace: "personal-q3k" dns: "foo.q3k.org"
+//  }
+//  allow_domain {
+//    namespace: "personal-q3k" dns: "bar.q3k.org"
+//  }
+//
+message Config {
+    // List of domains that are allowed to be configured as
+    // ingresses in a given namespace. If a domain does not
+    // appear in this list, it will be allowed to run in any
+    // namespace.
+    repeated AllowDomain allow_domain = 1;
+}
+
+message AllowDomain {
+    // namespace is a kubernetes namespace. An empty string is
+    // treated as the 'default' namespace.
+    string namespace = 1;
+    // dns is a domain name like 'example.com' or a wildcard
+    // like '*.foo.example.com'.
+    // Wildcards match domains at any level beneath the root,
+    // so the example above would match 'bar.foo.example.com'
+    // and 'baz.bar.foo.example.com'. However, they do not
+    // catch the root itself, ie. the above would not catch
+    // 'foo.example.com'.
+    string dns = 2;
+}
diff --git a/cluster/admitomatic/config/sample.pb.text b/cluster/admitomatic/config/sample.pb.text
new file mode 100644
index 0000000..21e98bc
--- /dev/null
+++ b/cluster/admitomatic/config/sample.pb.text
@@ -0,0 +1,7 @@
+allow_domain { namespace: "example" dns: "*.example.com" }
+allow_domain {
+  namespace: "personal-q3k" dns: "foo.q3k.org"
+}
+allow_domain {
+  namespace: "personal-q3k" dns: "bar.q3k.org"
+}
diff --git a/cluster/admitomatic/ingress.go b/cluster/admitomatic/ingress.go
index 42cab98..a1d57a5 100644
--- a/cluster/admitomatic/ingress.go
+++ b/cluster/admitomatic/ingress.go
@@ -1,10 +1,14 @@
 package main
 
 import (
+	"encoding/json"
 	"fmt"
 	"strings"
 
+	"github.com/golang/glog"
 	admission "k8s.io/api/admission/v1beta1"
+	networking "k8s.io/api/networking/v1beta1"
+	meta "k8s.io/apimachinery/pkg/apis/meta/v1"
 )
 
 // ingressFilter is a filter which allows or denies the creation of an ingress
@@ -125,6 +129,99 @@
 	if req.Kind.Group != "networking.k8s.io" || req.Kind.Kind != "Ingress" {
 		return nil, fmt.Errorf("not an ingress")
 	}
-	// TODO(q3k); implement
-	return nil, fmt.Errorf("unimplemented")
+
+	result := func(s string, args ...interface{}) (*admission.AdmissionResponse, error) {
+		res := &admission.AdmissionResponse{
+			UID: req.UID,
+		}
+		if s == "" {
+			res.Allowed = true
+		} else {
+			res.Allowed = false
+			res.Result = &meta.Status{
+				Code:    403,
+				Message: fmt.Sprintf("admitomatic: %s", fmt.Sprintf(s, args...)),
+			}
+		}
+		return res, nil
+	}
+
+	// Permit any actions on critical system namespaes. See:
+	// https://kubernetes.io/docs/reference/access-authn-authz/extensible-admission-controllers/
+	// “Avoiding operating on the kube-system namespace”
+	if req.Namespace == "kube-system" {
+		return result("")
+	}
+
+	switch req.Operation {
+	case "CREATE":
+	case "UPDATE":
+	default:
+		// We only care about creations/updates, everything else is referred to plain RBAC.
+		return result("")
+	}
+
+	ingress := networking.Ingress{}
+	err := json.Unmarshal(req.Object.Raw, &ingress)
+	if err != nil {
+		glog.Errorf("Unmarshaling Ingress failed: %v", err)
+		return result("invalid object")
+	}
+
+	// Check TLS config for hosts.
+	for j, t := range ingress.Spec.TLS {
+		for k, h := range t.Hosts {
+			if strings.Contains(h, "*") {
+				// TODO(q3k): support wildcards
+				return result("wildcard host %q (%d in TLS entry %d) is not permitted", h, k, j)
+			}
+			if !i.domainAllowed(req.Namespace, h) {
+				return result("host %q (%d) in TLS entry %d is not allowed in namespace %q", h, k, j, req.Namespace)
+			}
+		}
+	}
+
+	// Check rules for hosts.
+	for j, r := range ingress.Spec.Rules {
+		h := r.Host
+		// Per IngressRule spec:
+		//   If the host is unspecified, the Ingress routes all traffic based
+		//   on the specified IngressRuleValue. Host can be "precise" which is
+		//   a domain name without the terminating dot of a network host (e.g.
+		//   "foo.bar.com") or "wildcard", which is a domain name prefixed with
+		//   a single wildcard label (e.g. "*.foo.com").
+		//
+		// We reject everything other than precise hosts.
+		if h == "" {
+			return result("empty host %q (in rule %d) is not permitted", h, j)
+		}
+		if strings.Contains(h, "*") {
+			// TODO(q3k): support wildcards
+			return result("wildcard host %q (in rule %d) is not permitted", h, j)
+		}
+		if !i.domainAllowed(req.Namespace, h) {
+			return result("host %q (in rule %d) is not allowed in namespace %q", h, j, req.Namespace)
+		}
+	}
+
+	// Only allow a trusted subset of n-i-c annotations.
+	// TODO(q3k): allow opt-out for some namespaces
+	allowed := map[string]bool{
+		"proxy-body-size":  true,
+		"ssl-redirect":     true,
+		"backend-protocol": true,
+	}
+	prefix := "nginx.ingress.kubernetes.io/"
+	for k, _ := range ingress.Annotations {
+		if !strings.HasPrefix(k, prefix) {
+			continue
+		}
+		k = strings.TrimPrefix(k, prefix)
+		if !allowed[k] {
+			return result("forbidden annotation %q", k)
+		}
+	}
+
+	// All clear, accept this Ingress.
+	return result("")
 }
diff --git a/cluster/admitomatic/ingress_test.go b/cluster/admitomatic/ingress_test.go
index 91cf2b9..15a6049 100644
--- a/cluster/admitomatic/ingress_test.go
+++ b/cluster/admitomatic/ingress_test.go
@@ -1,6 +1,15 @@
 package main
 
-import "testing"
+import (
+	"encoding/json"
+	"strings"
+	"testing"
+
+	admission "k8s.io/api/admission/v1beta1"
+	networking "k8s.io/api/networking/v1beta1"
+	meta "k8s.io/apimachinery/pkg/apis/meta/v1"
+	runtime "k8s.io/apimachinery/pkg/runtime"
+)
 
 func TestPatterns(t *testing.T) {
 	f := ingressFilter{}
@@ -76,3 +85,121 @@
 		}
 	}
 }
+
+func TestIngressPermitted(t *testing.T) {
+	f := ingressFilter{}
+	// Errors discarded, tested in TestPatterns.
+	f.allow("matrix", "matrix.hackerspace.pl")
+	f.allow("ceph-waw3", "*.hackerspace.pl")
+	f.allow("personal-q3k", "*.k0.q3k.org")
+	f.allow("personal-vuko", "shells.vuko.pl")
+	f.allow("minecraft", "*.k0.q3k.org")
+
+	mkReq := func(ns string, annotations map[string]string, is *networking.IngressSpec) *admission.AdmissionRequest {
+		i := &networking.Ingress{
+			Spec: *is,
+		}
+		i.Annotations = annotations
+		raw, err := json.Marshal(i)
+		if err != nil {
+			t.Fatalf("marshaling test ingress: %v", err)
+		}
+		return &admission.AdmissionRequest{
+			UID: "test",
+			Kind: meta.GroupVersionKind{
+				Group:   "networking.k8s.io",
+				Version: "v1beta1",
+				Kind:    "Ingress",
+			},
+			Namespace: ns,
+			Operation: "CREATE",
+			Object: runtime.RawExtension{
+				Raw: raw,
+			},
+		}
+	}
+
+	for i, el := range []struct {
+		req *admission.AdmissionRequest
+		err string
+	}{
+		// 0: unrelated domain, should be allowed
+		{mkReq("default", nil, &networking.IngressSpec{
+			Rules: []networking.IngressRule{
+				{Host: "example.com"},
+			},
+			TLS: []networking.IngressTLS{
+				{
+					Hosts: []string{"example.com"},
+				},
+			},
+		}), ""},
+		// 1: permitted restricted domain, should be allowed
+		{mkReq("matrix", nil, &networking.IngressSpec{
+			Rules: []networking.IngressRule{
+				{Host: "matrix.hackerspace.pl"},
+			},
+			TLS: []networking.IngressTLS{
+				{
+					Hosts: []string{"matrix.hackerspace.pl"},
+				},
+			},
+		}), ""},
+		// 2: forbidden restricted domain, should be rejected
+		{mkReq("personal-hacker", nil, &networking.IngressSpec{
+			Rules: []networking.IngressRule{
+				{Host: "matrix.hackerspace.pl"},
+			},
+			TLS: []networking.IngressTLS{
+				{
+					Hosts: []string{"matrix.hackerspace.pl"},
+				},
+			},
+		}), "not allowed in namespace"},
+		// 3: weird ingress but okay
+		{mkReq("personal-hacker", nil, &networking.IngressSpec{}), ""},
+		// 4: janky annotations, should be rejected
+		{mkReq("matrix", map[string]string{
+			"nginx.ingress.kubernetes.io/configuration-snippet": "omghax",
+		}, &networking.IngressSpec{
+			Rules: []networking.IngressRule{
+				{Host: "matrix.hackerspace.pl"},
+			},
+			TLS: []networking.IngressTLS{
+				{
+					Hosts: []string{"matrix.hackerspace.pl"},
+				},
+			},
+		}), "forbidden annotation"},
+		// 5: accepted annotations, should be allowed
+		{mkReq("matrix", map[string]string{
+			"nginx.ingress.kubernetes.io/proxy-body-size": "2137",
+			"foo.q3k.org/bar": "baz",
+		}, &networking.IngressSpec{
+			Rules: []networking.IngressRule{
+				{Host: "matrix.hackerspace.pl"},
+			},
+			TLS: []networking.IngressTLS{
+				{
+					Hosts: []string{"matrix.hackerspace.pl"},
+				},
+			},
+		}), ""},
+	} {
+		res, err := f.admit(el.req)
+		if err != nil {
+			t.Errorf("test %d: admit: %v", i, err)
+		}
+		if el.err == "" {
+			if !res.Allowed {
+				t.Errorf("test %d: wanted allow, got %q", i, res.Result.Message)
+			}
+		} else {
+			if res.Allowed {
+				t.Errorf("test %d: wanted %q, got allowed", i, el.err)
+			} else if !strings.Contains(res.Result.Message, el.err) {
+				t.Errorf("test %d: wanted %q, got %q", i, el.err, res.Result.Message)
+			}
+		}
+	}
+}
diff --git a/cluster/admitomatic/main.go b/cluster/admitomatic/main.go
index 3178818..b05ff2f 100644
--- a/cluster/admitomatic/main.go
+++ b/cluster/admitomatic/main.go
@@ -3,6 +3,7 @@
 import (
 	"context"
 	"flag"
+	"io/ioutil"
 	"net/http"
 	"time"
 
@@ -11,13 +12,29 @@
 )
 
 var (
-	flagListen = "127.0.0.1:8080"
+	flagListen  = "127.0.0.1:8080"
+	flagConfig  = ""
+	flagTLSKey  = ""
+	flagTLSCert = ""
 )
 
 func main() {
-	flag.StringVar(&flagListen, "pub_listen", flagListen, "Address to listen on for HTTP traffic")
+	flag.StringVar(&flagListen, "admitomatic_listen", flagListen, "Address to listen on for HTTP traffic")
+	flag.StringVar(&flagTLSKey, "admitomatic_tls_key", flagTLSKey, "TLS key to serve HTTP with")
+	flag.StringVar(&flagTLSCert, "admitomatic_tls_cert", flagTLSCert, "TLS certificate to serve HTTP with")
+	flag.StringVar(&flagConfig, "admitomatic_config", flagConfig, "Config path (prototext format)")
 	flag.Parse()
 
+	if flagConfig == "" {
+		glog.Exitf("-admitomatic_config must be set")
+	}
+	if flagTLSKey == "" {
+		glog.Exitf("-admitomatic_tls_key must be set")
+	}
+	if flagTLSCert == "" {
+		glog.Exitf("-admitomatic_tls_cert must be set")
+	}
+
 	m := mirko.New()
 	if err := m.Listen(); err != nil {
 		glog.Exitf("Listen(): %v", err)
@@ -27,13 +44,24 @@
 		glog.Exitf("Serve(): %v", err)
 	}
 
+	configData, err := ioutil.ReadFile(flagConfig)
+	if err != nil {
+		glog.Exitf("Could not read config: %v", err)
+	}
+
+	s, err := newService(configData)
+	if err != nil {
+		glog.Exitf("Could not start service: %v", err)
+	}
+
 	mux := http.NewServeMux()
+	mux.HandleFunc("/", s.handler)
 	// TODO(q3k): implement admission controller
 	srv := &http.Server{Addr: flagListen, Handler: mux}
 
 	glog.Infof("Listening on %q...", flagListen)
 	go func() {
-		if err := srv.ListenAndServe(); err != nil {
+		if err := srv.ListenAndServeTLS(flagTLSCert, flagTLSKey); err != nil {
 			glog.Error(err)
 		}
 	}()
diff --git a/cluster/admitomatic/service.go b/cluster/admitomatic/service.go
new file mode 100644
index 0000000..8fa2698
--- /dev/null
+++ b/cluster/admitomatic/service.go
@@ -0,0 +1,105 @@
+package main
+
+import (
+	"encoding/json"
+	"fmt"
+	"io/ioutil"
+	"net/http"
+
+	"github.com/golang/glog"
+	"google.golang.org/protobuf/encoding/prototext"
+	admission "k8s.io/api/admission/v1beta1"
+	meta "k8s.io/apimachinery/pkg/apis/meta/v1"
+
+	pb "code.hackerspace.pl/hscloud/cluster/admitomatic/config"
+)
+
+type service struct {
+	ingress ingressFilter
+}
+
+// newService creates an admitomatic service from a given prototext config.
+func newService(configuration []byte) (*service, error) {
+	var cfg pb.Config
+	if err := prototext.Unmarshal(configuration, &cfg); err != nil {
+		return nil, fmt.Errorf("parsing config: %v", err)
+	}
+
+	s := service{}
+
+	for i, ad := range cfg.AllowDomain {
+		if ad.Namespace == "" {
+			ad.Namespace = "default"
+		}
+		if ad.Dns == "" {
+			return nil, fmt.Errorf("config entry %d: dns must be set", i)
+		}
+		if err := s.ingress.allow(ad.Namespace, ad.Dns); err != nil {
+			return nil, fmt.Errorf("config entry %d: %v", i, err)
+		}
+		glog.Infof("Ingress: allowing %s in %s", ad.Dns, ad.Namespace)
+	}
+	return &s, nil
+}
+
+// handler is the main HTTP handler of the admitomatic service. It servers the
+// AdmissionReview API, and is called by the Kubernetes API server to
+// permit/deny creation/updating of resources.
+func (s *service) handler(w http.ResponseWriter, r *http.Request) {
+	var body []byte
+	if r.Body != nil {
+		if data, err := ioutil.ReadAll(r.Body); err == nil {
+			body = data
+		}
+	}
+
+	if r.Method != "POST" {
+		glog.Errorf("%s %s: invalid method", r.Method, r.URL)
+		return
+	}
+
+	contentType := r.Header.Get("Content-Type")
+	if contentType != "application/json" {
+		glog.Errorf("%s %s: invalid content-type", r.Method, r.URL)
+		return
+	}
+
+	var review admission.AdmissionReview
+	if err := json.Unmarshal(body, &review); err != nil {
+		glog.Errorf("%s %s: cannot decode: %v", r.Method, r.URL, err)
+		return
+	}
+
+	if review.Kind != "AdmissionReview" {
+		glog.Errorf("%s %s: invalid Kind (%q)", r.Method, r.URL, review.Kind)
+		return
+	}
+
+	var err error
+	req := review.Request
+	resp := &admission.AdmissionResponse{
+		UID:     req.UID,
+		Allowed: true,
+	}
+	switch {
+	case req.Kind.Group == "networking.k8s.io" && req.Kind.Kind == "Ingress":
+		resp, err = s.ingress.admit(req)
+		if err != nil {
+			glog.Errorf("%s %s %s: %v", req.Operation, req.Name, req.Namespace, err)
+			// Fail safe.
+			// TODO(q3k): monitor this?
+			resp = &admission.AdmissionResponse{
+				UID:     req.UID,
+				Allowed: false,
+				Result: &meta.Status{
+					Code:    500,
+					Message: "admitomatic: internal server error",
+				},
+			}
+		}
+	}
+
+	glog.Infof("%s %s %s in %s: %v (%v)", req.Operation, req.Kind.Kind, req.Name, req.Namespace, resp.Allowed, resp.Result)
+	review.Response = resp
+	json.NewEncoder(w).Encode(review)
+}