Error map
actively refused it HttpRequestException: No connection could be made because the target machine actively refused it (localhost:5001)
.NET · layer 4, Application & API
Centre: this error. First ring: errors it is linked with (12). Outer ring: what those are linked with. Colours show the layer of a request each error belongs to. Click any dot to re-centre the map on it; hover to follow its connections. The centre dot opens the error page.
Directly related (12)
Failed to create pod sandbox: plugin type="calico" failed (add): ... (FailedCreatePodSandBox)
The kubelet couldn’t set up the pod’s network sandbox — almost always a CNI plugin problem or exhausted pod IPs.
spec.ports[0].nodePort: Invalid value: 80: provided port is not in the valid range. The range of valid ports is 30000-32767
A NodePort Service asked for a port outside the cluster’s NodePort range (default 30000–32767).
Error response from daemon: Pool overlaps with other one on this address space
Docker tried to create a network whose subnet clashes with an existing Docker network (or a VPN/host route).
TaskCanceledException: The request was canceled due to the configured HttpClient.Timeout of 100 seconds elapsing
The HTTP call took longer than HttpClient.Timeout (100 s default), so .NET cancelled it.
driver failed programming external connectivity on endpoint: iptables: No chain/target/match by that name
Docker’s iptables rules were wiped (firewalld/ufw reload, iptables flush) while Docker was running, so it can’t publish ports.
System.Text.Json: '<' is an invalid start of a value. Path: $ | LineNumber: 0 | BytePositionInLine: 0
The response wasn’t JSON — usually an HTML error page, login redirect, or an empty body was passed to the JSON deserializer.
android.os.NetworkOnMainThreadException
The app made a network call on the main (UI) thread, which Android forbids.
Error response from daemon: network X not found
The container or Compose project refers to a Docker network that doesn’t exist (any more).
DNS not working inside a Kubernetes pod (could not resolve host / nslookup: can't resolve)
Pods can’t resolve service names or external hosts — CoreDNS is down, blocked by NetworkPolicy, or the upstream resolver fails.
System.IO.IOException: Failed to bind to address http://127.0.0.1:5000: address already in use
Kestrel can’t listen because another process (often a previous run of the same app) uses the port.
Error: connect ECONNREFUSED 127.0.0.1:5432
Nothing is listening at that host:port — the target service is down or you’re connecting to the wrong address.
Ingress returns "404 Not Found" / "default backend - 404" (ingress-nginx)
The ingress controller received the request but no Ingress rule matched the host/path, so it answered with its default backend.
Two steps away (36)
Kubernetes: Pod Evicted — The node was low on resource: memory / ephemeral-storage
The kubelet removed the pod because its node ran short of memory or disk.
ECS task stopped: CannotPullContainerError: pull image manifest has been retried ... / ref pull has been retried
The ECS task couldn’t pull its image — no network route to the registry, missing ECR permissions, or a wrong image tag.
Kubernetes node NotReady (Kubelet stopped posting node status)
The control plane hasn’t heard from a node’s kubelet, or the kubelet reports a problem — pods there stop being scheduled and are…
Service has no endpoints (no endpoints available for service / Endpoints: <none>)
The Service’s selector matches no ready pods, so traffic to it is refused or returns 503.
Job for nginx.service failed because the control process exited with error code
systemd tried to start the service, but its start command failed. The real reason is in the service’s status/journal.
Failed to start x.service: Unit x.service not found
systemd has no unit with that name — the package isn’t installed, the name differs on this distro, or a new unit file wasn’t load…
docker compose: services.x Additional property y is not allowed / yaml: line N: mapping values are not allowed
The compose file is invalid YAML or uses a key Compose doesn’t recognise at that level (usually an indentation mistake).
docker-compose: command not found / 'compose' is not a docker command
Your system has only one of the two Compose flavours: the old docker-compose (v1) binary or the newer docker compose (v2) plugin.
service "web" depends on undefined service "db": invalid compose project
A service lists depends_on (or links/networks) for a service name that isn’t defined in the Compose file(s) being used.
MySQL ERROR 2006 (HY000): MySQL server has gone away
The connection to MySQL was closed — usually by a timeout or a packet larger than `max_allowed_packet`.
HTTP 408 Request Timeout
The server closed the connection because the client took too long to send the complete request.
HTTP 504 Gateway Timeout
A proxy or gateway waited too long for the upstream server to respond and gave up.
Error: listen EADDRINUSE: address already in use :::3000
Another process is already listening on that port.
Docker: Bind for 0.0.0.0:80 failed: port is already allocated
Another container or host process already publishes that host port.
Cloudflare Error 1020: Access Denied
A Cloudflare firewall/WAF custom rule blocked the request — the visitor’s IP, country, user agent or request pattern matched a bl…
SyntaxError: Unexpected token < in JSON at position 0
`JSON.parse()` / `response.json()` received something that isn’t JSON — very often an HTML error page.
com.fasterxml.jackson.databind.exc.MismatchedInputException: Cannot deserialize value of type `java.util.ArrayList` from Object value
Jackson found JSON whose shape doesn’t match the target Java type (object vs array, string vs number, missing constructor).
com.fasterxml.jackson.databind.exc.UnrecognizedPropertyException: Unrecognized field "x", not marked as ignorable
The JSON contains a field your Java class doesn’t have, and Jackson is configured to fail on unknown properties.
CalledFromWrongThreadException: Only the original thread that created a view hierarchy can touch its views
Background code updated a View directly; UI changes must happen on the main thread.
ANR: Application Not Responding (Input dispatching timed out)
The main thread was blocked for about 5 seconds (input) or a broadcast/service took too long, so Android showed “App isn’t respon…
Room: Cannot access database on the main thread since it may potentially lock the UI for a long period of time
A Room DAO query ran on the main thread; Room forbids it by default.
WARN: the attribute `version` is obsolete, it will be ignored
A harmless Compose v2 warning: the top-level version: line in docker-compose.yml is no longer used.
Docker container is unhealthy (health check failing)
The container is running, but its HEALTHCHECK command keeps failing, so Docker (and dependent services) consider it unhealthy.
Error Domain=NSURLErrorDomain Code=-1009 "The Internet connection appears to be offline."
URLSession couldn’t reach the network — the device is offline, the app’s cellular data is disabled, or the simulator lost network…
Error: getaddrinfo ENOTFOUND host / Name or service not known
DNS lookup for the hostname failed — the name is wrong, doesn’t exist, or this machine can’t resolve it.
net::ERR_NAME_NOT_RESOLVED (This site can't be reached — server IP address could not be found)
DNS couldn’t resolve the hostname in the browser.
cURL error 6: Could not resolve host: api.example.com
PHP cURL couldn’t resolve the hostname via DNS.
Web server failed to start. Port 8080 was already in use.
Spring Boot couldn’t bind its embedded server port because another process uses it.
Error: listen EACCES: permission denied 0.0.0.0:80
Node isn’t allowed to bind that port — ports below 1024 need root on Linux/macOS, and some Windows ports are reserved.
LOG: could not bind IPv4 address "0.0.0.0": Address already in use — Is another postmaster already running on port 5432?
Another process (often a second PostgreSQL install or a container) already listens on 5432.
MySQL ERROR 2002 (HY000): Can't connect to local MySQL server through socket
The client couldn’t reach the MySQL server — it isn’t running, or the client is looking for the socket/port in the wrong place.
TypeError: Failed to fetch / NetworkError when attempting to fetch resource
The browser couldn’t complete the request at the network level — CORS, DNS, offline, blocked mixed content, or the server refused…
API Request Timed Out (ETIMEDOUT / ReadTimeout / timeout of 30000ms exceeded)
The client gave up waiting — either for the connection to open or for the response to arrive.
HTTP 404 Not Found
The server can’t find anything at the requested URL.
Error from server: admission webhook "validate.nginx.ingress.kubernetes.io" denied the request
A validating admission webhook (ingress-nginx, Gatekeeper/OPA, Kyverno) inspected your object and rejected it; the reason follows…
Error Domain=NSURLErrorDomain Code=-1001 "The request timed out."
The server didn’t respond within URLSession’s timeout (60 s default) — slow server, unreachable host on this network, or a stalle…
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