A container may log to the journal (hq ADR 0179)

A jail reads a log; a container's output went to a file of the runtime's own under a path that
changes on recreate, so no jail could read a container's service. logging: journald runs the
container with the journal as its driver, named in the spec so moving it recreates it; any other
place is refused.

internal/declaration/declaration.go

@@ -952,6 +952,14 @@ type Container struct {
 	// container; a privileged container stays undeclarable.
 	Capabilities []string `json:"capabilities,omitempty"`
 
+	// Logging names where the runtime sends this container's output: "journald" sends it to the
+	// machine's journal, under the container's name, where what reads the machine's logs — its
+	// intrusion prevention first of all (novox/hq ADR 0179) — can read it the way it reads the
+	// machine's own services. Empty keeps the runtime's default, which is a file of the runtime's
+	// own that nothing but the runtime reads. Part of the spec: a container that logs elsewhere
+	// is a different container, and the runtime cannot change a running one's driver.
+	Logging string `json:"logging,omitempty"`
+
 	// Networks are networks this container also joins once created, by name — a found network a
 	// per-machine setting keeps for a taken container (novox/hq ADR 0163, rule 4), so a
 	// neighbour that resolves it there keeps resolving it until the neighbour is taken too.
@@ -1057,6 +1065,10 @@ func (c *Container) validate(where string, _ bool) []string {
 				"capability's name (CAP_NET_ADMIN or NET_ADMIN)")
 		}
 	}
+	if c.Logging != "" && c.Logging != "journald" {
+		problems = append(problems, where+": logging is "+strconv.Quote(c.Logging)+", and the only place a "+
+			"container's output can be sent besides the runtime's own file is \"journald\"")
+	}
 	for _, n := range c.Networks {
 		problems = append(problems, (&Network{Name: n}).validate(where+": networks", false)...)
 		if n == c.Network {

internal/declaration/declaration_test.go

@@ -524,3 +524,24 @@ func TestACapabilityIsNamedOrRefused(t *testing.T) {
 		}
 	}
 }
+
+// A container may send its output to the machine's journal, and nowhere else but the runtime's own
+// file (novox/hq ADR 0179): what reads the machine's logs then reads the container's too.
+func TestAContainerMayLogToTheJournalAndNowhereElse(t *testing.T) {
+	image := "postgres@sha256:" + strings.Repeat("a", 64)
+	d, err := Parse([]byte(`{"declaration":1,"resources":[
+	  {"id":"front","type":"container","name":"front","image":"` + image + `","logging":"journald"}
+	]}`))
+	if err != nil {
+		t.Fatal(err)
+	}
+	if got := d.Resources[0].(*Container).Logging; got != "journald" {
+		t.Fatalf("logging read as %q", got)
+	}
+	for _, bad := range []string{`"syslog"`, `"none"`, `"json-file"`} {
+		if _, err := Parse([]byte(`{"declaration":1,"resources":[
+		  {"id":"front","type":"container","name":"front","image":"` + image + `","logging":` + bad + `}]}`)); err == nil {
+			t.Errorf("%s was accepted as a place to log", bad)
+		}
+	}
+}