fix DNS timeout error not retried (#2300)

Author: a-canya

.changelog/63caeb72930c4d84bbab8d36fe10d4b5.json

@@ -0,0 +1,8 @@
+{
+    "id": "63caeb72-930c-4d84-bbab-8d36fe10d4b5",
+    "type": "bugfix",
+    "description": "Improve recognition of retryable DNS errors.",
+    "modules": [
+        "."
+    ]
+}

aws/retry/retryable_error.go

@@ -97,11 +97,21 @@ func (r RetryableConnectionError) IsErrorRetryable(err error) aws.Ternary {
 	var netOpErr *net.OpError
 	var dnsError *net.DNSError
 
-	switch {
-	case errors.As(err, &dnsError):
+	if errors.As(err, &dnsError) {
 		// NXDOMAIN errors should not be retried
-		retryable = !dnsError.IsNotFound && dnsError.IsTemporary
+		if dnsError.IsNotFound {
+			return aws.BoolTernary(false)
+		}
+
+		// if !dnsError.Temporary(), error may or may not be temporary,
+		// (i.e. !Temporary() =/=> !retryable) so we should fall through to
+		// remaining checks
+		if dnsError.Temporary() {
+			return aws.BoolTernary(true)
+		}
+	}
 
+	switch {
 	case errors.As(err, &conErr) && conErr.ConnectionError():
 		retryable = true
 

aws/retry/retryable_error_test.go

@@ -262,3 +262,47 @@ func TestCanceledError(t *testing.T) {
 		})
 	}
 }
+
+func TestDNSError(t *testing.T) {
+	cases := map[string]struct {
+		Err    error
+		Expect aws.Ternary
+	}{
+		"IsNotFound": {
+			Err: &net.DNSError{
+				IsNotFound: true,
+			},
+			Expect: aws.FalseTernary,
+		},
+		"Temporary (IsTimeout)": {
+			Err: &net.DNSError{
+				IsTimeout: true,
+			},
+			Expect: aws.TrueTernary,
+		},
+		"Temporary (IsTemporary)": {
+			Err: &net.DNSError{
+				IsTemporary: true,
+			},
+			Expect: aws.TrueTernary,
+		},
+		"Temporary() == false but it falls through": {
+			Err: &net.OpError{
+				Op:  "dial",
+				Err: &net.DNSError{},
+			},
+			Expect: aws.TrueTernary,
+		},
+	}
+
+	for name, c := range cases {
+		t.Run(name, func(t *testing.T) {
+			var r RetryableConnectionError
+
+			retryable := r.IsErrorRetryable(c.Err)
+			if e, a := c.Expect, retryable; e != a {
+				t.Errorf("expect %v retryable, got %v", e, a)
+			}
+		})
+	}
+}