Why Caddy Gives 502 When the Backend Works Fine by IP
A 502 usually means the browser-to-Caddy leg worked and the Caddy-to-upstream leg did not.
TOPIC
Caddy & Reverse Proxy
Lessons, explainers, experiments, and implementation notes.
Inside a Caddy Container, localhost Is Caddy — Not Your App
The most common Docker reverse-proxy mistake is technically valid networking aimed at the wrong namespace.
When a Docker Service Name Does Not Resolve from Caddy
Docker DNS only resolves service names inside the networks where those services actually meet.
Caddy Can Reach the HTTPS Upstream and Still Fail the TLS Handshake
An IP can be the correct route to an upstream while being the wrong identity for its certificate.
After a Caddy Upgrade, Why Did My HTTPS Upstream Start Seeing a Different Host?
Caddy 2.11 changed default Host behavior for HTTPS upstreams, exposing apps that relied on the old value.
The Web UI Loads Through Caddy but Live Updates Never Connect
Normal HTTP can succeed while a WebSocket upgrade fails on the same application.
Why an App Works on a Subdomain but Breaks Under /app
Stripping a prefix is easy; making the application believe it lives under that prefix is harder.
Your SPA Homepage Works Through Caddy, but Refreshing /settings Returns 404
Client-side routes exist only after index.html loads; the server still needs a fallback for direct requests.
Why Your API Suddenly Returns index.html Through Caddy
A catch-all frontend fallback can hide backend routing mistakes behind a successful HTML response.
The Tiny Trailing-Slash Rule That Creates Big Redirect Loops
External redirects, internal rewrites and upstream canonicalization are different tools even when they change the same path.
Cloudflare Tunnel Reaches Caddy but Still Returns 502
The failing TLS identity may be on the Cloudflare-to-origin leg rather than in Caddy's upstream proxy.
Why Every Request Looks Like It Came from Cloudflare Instead of the User
Original client IP is trustworthy only when Caddy knows which proxy was allowed to write it.
Why Caddy Will Not Issue a Wildcard Certificate with the Normal HTTP Challenge
Wildcard ACME certificates require DNS validation of the parent zone.
The Caddyfile Says dns cloudflare, but Caddy Says the Module Does Not Exist
DNS challenge syntax only works when the running binary contains that provider module.
Caddy Automatic HTTPS Cannot Fix a Port 80/443 Ownership Problem
ACME automation still depends on the challenge traffic reaching the Caddy instance that requested the certificate.
Caddy tls internal Works — So Why Does the Browser Still Say Untrusted?
Private TLS is only trusted by clients that possess and trust the private root CA.
How I Proxy from One Caddy to Another Without tls_insecure_skip_verify
Internal HTTPS between proxies is useful only when the caller can verify the upstream identity.
Why handle_errors Does Not Catch the 502 Your Upstream Returned
A proxied 5xx status is a response, not automatically a Caddy handler error.
Forward Auth Works, Then the Browser Gets Stuck in a Login Redirect Loop
Auth gateways need the original request context to decide and redirect correctly.
Do Not Trust a User Identity Header Just Because Caddy Forwarded It
Identity headers are safe only when clients cannot inject equivalent values around the auth boundary.
One Hostname, Some Public Paths, Some Private Paths: Make the Boundary Obvious
Path-based access control is safest when protected and public branches cannot accidentally fall through.
Your Caddy Admin API Is a Deployment Interface - Treat It Like Root
The admin endpoint can replace active configuration, so broad exposure changes the security boundary of the edge.
When the Caddyfile Becomes Copy-Paste Infrastructure
Repeated auth, TLS and header policy drifts when every site block is cloned by hand.
Caddy Says My Upstream Is Unhealthy, but the App Is Fine
A synthetic health request measures the service only if it looks like a request the service considers valid.
Proxy Retries Can Save a GET and Duplicate a POST
Retry policy is also application semantics: replaying a write may repeat a side effect.
The Intermittent 502 That Appears Only After a Connection Has Been Idle
Keepalive timeout mismatches can fail a request even while proxy and backend are otherwise healthy.
Three Caddy Instances Can All Be Healthy While Nobody Knows Which One Owns the Request
Multiple proxies are fine when each boundary has one explicit owner.
Stop Restarting Caddy to Apply a Caddyfile Change
Caddy has graceful config reloads; restarting the process turns a routing edit into avoidable downtime.
Caddy Logs Exist, but They Still Do Not Answer Which User Request Failed
Logs become useful when access records, proxy errors and request identity can be correlated.
How I Know Caddy Is Healthy but One Upstream Is Not
The edge process can be green while one proxied service is failing behind it.