azure: retry HTTP requests on codes 404, 410, and 429

docs/release-notes.md

@@ -23,6 +23,7 @@ nav_order: 9
 ### Bug fixes
 
 - Fix failure when config only disables units already disabled
+- Retry HTTP requests on Azure on status codes 404, 410, and 429
 
 
 ## Ignition 2.17.0 (2023-11-20)

internal/providers/azure/azure.go

@@ -112,7 +112,16 @@ func fetchFromIMDS(f *resource.Fetcher) ([]byte, error) {
 	headers := make(http.Header)
 	headers.Set("Metadata", "true")
 
-	data, err := f.FetchToBuffer(imdsUserdataURL, resource.FetchOptions{Headers: headers})
+	// Azure IMDS expects some codes <500 to still be retried...
+	// Here, we match the cloud-init set.
+	// https://github.com/canonical/cloud-init/commit/c1a2047cf291
+	// https://github.com/coreos/ignition/issues/1806
+	retryCodes := []int{
+		404, // not found
+		410, // gone
+		429, // rate-limited
+	}
+	data, err := f.FetchToBuffer(imdsUserdataURL, resource.FetchOptions{Headers: headers, RetryCodes: retryCodes})
 	if err != nil {
 		return nil, fmt.Errorf("fetching to buffer: %w", err)
 	}

internal/resource/http.go

@@ -263,6 +263,21 @@ func (f *Fetcher) newHttpClient() error {
 	return nil
 }
 
+func shouldRetryHttp(statusCode int, opts FetchOptions) bool {
+	// we always retry 500+
+	if statusCode >= 500 {
+		return true
+	}
+
+	for _, retryCode := range opts.RetryCodes {
+		if statusCode == retryCode {
+			return true
+		}
+	}
+
+	return false
+}
+
 // httpReaderWithHeader performs an HTTP request on the provided URL with the
 // provided request header & method and returns the response body Reader, HTTP
 // status code, a cancel function for the result's context, and error (if any).
@@ -298,7 +313,7 @@ func (c HttpClient) httpReaderWithHeader(opts FetchOptions, url string) (io.Read
 
 		if err == nil {
 			c.logger.Info("%s result: %s", opts.HTTPVerb, http.StatusText(resp.StatusCode))
-			if resp.StatusCode < 500 {
+			if !shouldRetryHttp(resp.StatusCode, opts) {
 				return resp.Body, resp.StatusCode, cancelFn, nil
 			}
 			resp.Body.Close()

internal/resource/url.go

@@ -131,6 +131,10 @@ type FetchOptions struct {
 	// LocalPort is a function returning a local port used to establish the TCP connection.
 	// Most of the time, letting the Kernel choose a random port is enough.
 	LocalPort func() int
+
+	// List of HTTP codes to retry that usually would be considered as complete.
+	// Status codes >= 500 are always retried.
+	RetryCodes []int
 }
 
 // FetchToBuffer will fetch the given url into a temporary file, and then read