Traefik Rewrite Body Compression

Traefik Rewrite-Body Plugin Compression Fix

Problem

The packruler/rewrite-body Traefik plugin (used for injecting analytics scripts like rybbit into HTML responses) fails to decompress gzip-compressed responses from backends. Despite the monitoring.types = ["text/html"] filter, the plugin attempts to decompress ALL responses before checking content type. When decompression fails, it corrupts the response body, breaking:

• WebSocket upgrade handshakes
• Authentication flows (HA Companion app's external_auth callback)
• Mobile app connectivity (while browser appears to work due to auto-reconnect)

Context / Trigger Conditions

• Traefik logs show: Rewrite-Body | ERROR ... Error loading content: flate: corrupt input before offset 5
• Mobile apps (e.g., Home Assistant Companion) fail while browser works
• HA Companion app shows repeated GET /?external_auth=1 requests (auth loop)
• WebSocket connections (/api/websocket) are very short-lived (seconds instead of minutes)
• HTTP 499 errors on API calls (client disconnects due to corrupted responses)
• Using packruler/rewrite-body plugin v1.2.0 with monitoring.types = ["text/html"]

Misleading Symptoms

• HTTP/3 (QUIC) may appear to be the cause because HTTP/3 requests show 499 errors. This is a red herring - the rewrite-body plugin corruption affects all protocols.
• WebSocket issues may look like a timeout or proxy configuration problem.
• The monitoring.types = ["text/html"] config suggests the plugin should only touch HTML, but it still processes all responses for decompression before filtering.

Solution

Step 1: Create a strip-accept-encoding middleware

Add a Traefik middleware that removes Accept-Encoding from requests, forcing backends to send uncompressed responses that the plugin can safely process:

# In traefik/middleware.tf
resource "kubernetes_manifest" "middleware_strip_accept_encoding" {
  manifest = {
    apiVersion = "traefik.io/v1alpha1"
    kind       = "Middleware"
    metadata = {
      name      = "strip-accept-encoding"
      namespace = kubernetes_namespace.traefik.metadata[0].name
    }
    spec = {
      headers = {
        customRequestHeaders = {
          "Accept-Encoding" = ""
        }
      }
    }
  }
  depends_on = [helm_release.traefik]
}

Step 2: Add middleware to routes with rewrite-body

In the ingress factory middleware chain, add strip-accept-encoding BEFORE the rewrite-body middleware:

var.rybbit_site_id != null ? "traefik-strip-accept-encoding@kubernetescrd" : null,
var.rybbit_site_id != null ? "${var.namespace}-rybbit-analytics-${var.name}@kubernetescrd" : null,

The order matters: strip-accept-encoding must come first so the request reaches the backend without Accept-Encoding, and the uncompressed response then passes through the rewrite-body plugin.

Verification

1. Check Traefik logs for absence of flate: corrupt input errors:

   kubectl logs -n traefik -l app.kubernetes.io/name=traefik --tail=200 | grep -i "flate\|rewrite-body"
   

2. Verify the middleware chain includes strip-accept-encoding before rybbit:

   kubectl get ingress -n <namespace> <name> -o jsonpath='{.metadata.annotations.traefik\.ingress\.kubernetes\.io/router\.middlewares}'
   

3. Test mobile app connectivity (HA Companion, etc.)

Notes

• This affects ALL services using the rewrite-body plugin, not just HA
• The fix is applied conditionally: strip-accept-encoding is only added to the middleware chain when rybbit_site_id is set, so services without analytics are unaffected
• Both ingress_factory and reverse_proxy/factory modules need the fix
• Traefik may still compress responses to clients via its own compression middleware; the strip only affects the backend request
• The plugin's monitoring.types filter works for deciding what to rewrite, but decompression is attempted on all responses regardless

See Also

• ingress-factory-migration - Covers the ingress factory module that creates rybbit analytics middlewares
• traefik-http3-quic - HTTP/3 configuration (not the cause, but often a red herring when debugging this issue)