Kubelet ignoring unknown envvars

comp/core/workloadmeta/collectors/internal/kubelet/kubelet.go

@@ -417,9 +417,18 @@ func extractEnvFromSpec(envSpec []kubelet.EnvVar) map[string]string {
 			continue
 		}
 
+		ok := true
 		runtimeVal := e.Value
 		if runtimeVal != "" {
-			runtimeVal = expansion.Expand(runtimeVal, mappingFunc)
+			runtimeVal, ok = expansion.Expand(runtimeVal, mappingFunc)
+		}
+
+		// Ignore environment variables that failed to expand
+		// This occurs when the env var references another env var
+		// that has its value sourced from an external source
+		// (eg. ConfigMap, Secret, DownwardAPI)
+		if !ok {
+			continue
 		}
 
 		env[e.Name] = runtimeVal

comp/core/workloadmeta/def/merge_test.go

@@ -49,6 +49,9 @@ func container1(testTime time.Time) Container {
 			Health:     ContainerHealthUnknown,
 		},
 		CollectorTags: []string{"tag1", "tag2"},
+		EnvVars: map[string]string{
+			"DD_SERVICE-partial": "my-svc",
+		},
 	}
 }
 
@@ -91,6 +94,10 @@ func container2() Container {
 			Health:     ContainerHealthHealthy,
 		},
 		CollectorTags: []string{"tag3"},
+		EnvVars: map[string]string{
+			"DD_SERVICE-partial": "my-svc",
+			"DD_ENV-extra":       "prod",
+		},
 	}
 }
 
@@ -114,6 +121,10 @@ func TestMerge(t *testing.T) {
 			ExitCode:   pointer.Ptr(int64(100)),
 			Health:     ContainerHealthHealthy,
 		},
+		EnvVars: map[string]string{
+			"DD_SERVICE-partial": "my-svc",
+			"DD_ENV-extra":       "prod",
+		},
 	}
 
 	expectedPorts := []ContainerPort{

internal/third_party/golang/expansion/expand.go

@@ -19,23 +19,23 @@ func syntaxWrap(input string) string {
 // implements the expansion semantics defined in the expansion spec; it
 // returns the input string wrapped in the expansion syntax if no mapping
 // for the input is found.
-func MappingFuncFor(context ...map[string]string) func(string) string {
-	return func(input string) string {
+func MappingFuncFor(context ...map[string]string) func(string) (string, bool) {
+	return func(input string) (string, bool) {
 		for _, vars := range context {
 			val, ok := vars[input]
 			if ok {
-				return val
+				return val, true
 			}
 		}
 
-		return syntaxWrap(input)
+		return syntaxWrap(input), false
 	}
 }
 
 // Expand replaces variable references in the input string according to
 // the expansion spec using the given mapping function to resolve the
 // values of variables.
-func Expand(input string, mapping func(string) string) string {
+func Expand(input string, mapping func(string) (string, bool)) (string, bool) {
 	var buf bytes.Buffer
 	checkpoint := 0
 	for cursor := 0; cursor < len(input); cursor++ {
@@ -52,7 +52,11 @@ func Expand(input string, mapping func(string) string) string {
 				// We were able to read a variable name correctly;
 				// apply the mapping to the variable name and copy the
 				// bytes into the buffer
-				buf.WriteString(mapping(read))
+				mappedValue, found := mapping(read)
+				if !found {
+					return "", false
+				}
+				buf.WriteString(mappedValue)
 			} else {
 				// Not a variable name; copy the read bytes into the buffer
 				buf.WriteString(read)
@@ -69,7 +73,7 @@ func Expand(input string, mapping func(string) string) string {
 
 	// Return the buffer and any remaining unwritten bytes in the
 	// input string.
-	return buf.String() + input[checkpoint:]
+	return buf.String() + input[checkpoint:], true
 }
 
 // tryReadVariableName attempts to read a variable name from the input