diff --git a/cluster/admitomatic/BUILD.bazel b/cluster/admitomatic/BUILD.bazel
index 5cb23ab..4d5aebc 100644
--- a/cluster/admitomatic/BUILD.bazel
+++ b/cluster/admitomatic/BUILD.bazel
@@ -12,6 +12,8 @@
         "//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",
     ],
 )
 
@@ -25,4 +27,10 @@
     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/ingress.go b/cluster/admitomatic/ingress.go
index 42cab98..298318f 100644
--- a/cluster/admitomatic/ingress.go
+++ b/cluster/admitomatic/ingress.go
@@ -1,10 +1,15 @@
 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 +130,99 @@
 	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)
+			}
+		}
+	}
+}