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This is the leading Docker-specific explanation, not a guaranteed diagnosis. A refused connection can have other causes, and the same error text has appeared in a historical Symfony report that was not a Docker setup.
What the error means in a Docker deployment
When Symfony uses KnpSnappyBundle to generate a PDF from a URL, the bundle starts wkhtmltopdf as a separate process and gives it the page URL to load. The HTTP request is made by wkhtmltopdf, not by the browser where you opened Symfony’s page and not necessarily by the PHP request handling the PDF job. The URL must resolve and accept connections from wherever that executable runs. KnpSnappyBundle also supports generating output directly from HTML, which is a different input path.
That distinction matters in Docker. Each container has its own network context. If wkhtmltopdf runs in a container, http://localhost/... means “this renderer container.” It does not mean the host, the PHP container, or another Compose service. Docker’s bridge-network documentation explains that containers attached to the same network can communicate with one another, while access from a different network is restricted by default. See Docker’s port publishing and mapping documentation.
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First establish these facts: the full URL passed to the bundle, the process or container in which wkhtmltopdf actually executes, the web server’s listening port, and whether that renderer can reach the URL. Do not start by changing PDF formatting flags: bundle settings for binary location, temporary files, or process timeout do not make a network endpoint reachable.
Find the renderer and the exact URL
Record the input Symfony gives the bundle
Inspect the code path that calls getOutput() or generate() and record the complete URL, including scheme, hostname, port, path, and any required authentication. Check whether the code passes a page URL or HTML directly. A URL that works from your laptop may fail from the renderer because DNS, routing, credentials, redirects, or the listening interface differ.
If the URL is built dynamically, log the final value in a safe development environment. Avoid logging access tokens or other credentials. Preserve the exact host and path for the connectivity test; replacing the hostname with an IP address can hide a DNS or virtual-host problem.
Identify where wkhtmltopdf executes
- Inside the Symfony/PHP container: use an address reachable from that container. If the web server is in the same container, its local listening address may be appropriate.
- Inside a separate renderer container: use the web service’s Docker network name and container port, provided both services share a network.
- On the Docker host: use an address the host process can route to. The service may need a published port, depending on how it is deployed.
- In a separate network: determine what routing, firewall rules, and DNS are available from that network rather than assuming Compose service names resolve there.
Symfony’s 7.4 Docker setup documentation covers a Symfony Docker setup, but actual host routing and network definitions vary by deployment and operating system.
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Run a request from the same container that launches wkhtmltopdf. This separates a network failure from a bundle configuration or PDF-rendering issue. The following examples are diagnostic procedures based on Docker’s documented network model; they are not claims about a tested deployment.
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- Open a shell in the renderer container. With Compose, a typical command is
docker compose exec renderer sh, replacingrendererwith the actual service name. If the container has no shell or request client, use an approved diagnostic image or add a client temporarily in a development environment. - Request the exact URL. If available, run
curl -v 'http://web:80/path'orwget -S -O /dev/null 'http://web:80/path'. Replace the example URL with the exact scheme, host, port, path, and authentication behavior used by the application. Do not put secrets directly in shell history. - Read the result. A refused connection means the connection did not reach a listener at that address and port. A name-resolution error points first to service naming or network DNS. An HTTP response—including a redirect, 401, or 404—shows that an HTTP server answered, but the requested page may still be inaccessible or unsuitable for the render.
- Compare the response with the app’s expected route. Check redirects, login requirements, reverse-proxy rules, and whether the application recognizes the requested hostname. If the probe succeeds but wkhtmltopdf fails, inspect wkhtmltopdf’s stderr and its request behavior separately.
Use the right address for your network layout
| Where wkhtmltopdf runs | Address to use | What must be true |
|---|---|---|
| Renderer and Symfony web server on a shared Docker bridge network | The web service’s network name and its container listening port, such as http://web:80/path when the service is named web and listens on port 80. |
Both containers are attached to the same network, and the web server listens on an interface reachable from the renderer. |
| Renderer runs on the Docker host | A host-reachable address and, where needed, the host-published port. | The service is published or otherwise routed to the host, and host firewall and bind settings allow the connection. |
| Renderer runs in a different container network | An address routed and resolvable from that network. | Explicit network connectivity or routing exists; a service name on an unrelated network is not enough. |
For two services on a shared bridge network, publishing the web port is generally unnecessary for container-to-container communication. Publishing maps a container port through the host; it is not the normal route between services already sharing a network. Docker notes that a published port can bind to all host addresses by default. If host access is required only through the host’s loopback interface, consider a loopback-only bind rather than exposing the port broadly. Follow your deployment’s security requirements when choosing a bind address.
Example Compose arrangement
This minimal illustration shows the relevant network relationship, not a complete Symfony or wkhtmltopdf deployment. Use your existing image, command, health checks, and network definitions as appropriate.
services:
web:
image: your-symfony-image
networks:
- app
renderer:
image: your-renderer-image
networks:
- app
networks:
app:
driver: bridgeIf the web process listens on port 80 inside its container, the renderer’s target would ordinarily use http://web:80/ on that shared network. Replace the service name and port with the actual ones. A host mapping such as ports: ["8080:80"] means host port 8080 forwards to container port 80; it does not change the container port the peer service ordinarily addresses on the shared network.
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Verify the listener and bind address
Confirm the web server is running and listening on the expected container port. A service can be “up” while its HTTP process is stopped, listening on another port, or bound only to an interface inaccessible from peers. Check the application and web-server logs, then inspect the listener from inside the web container if the necessary tools are available.
Check service name and network membership
Use the actual Docker or Compose service name visible to the renderer, not an assumed container name or a host-only DNS name. Confirm both services are attached to the same network. If they are on separate networks, connect them appropriately or use an explicitly routable address. A request from the host does not prove that a container can resolve or reach the same name.
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Check ports, proxies, redirects, and authentication
Use the port on which the web server listens inside its container when addressing a peer on the shared network. A host-published port is relevant to host-side access, not usually to that peer-to-peer path. Also check whether a reverse proxy expects a particular hostname, whether the application redirects to a public domain, and whether the PDF request needs a session cookie or other authentication. The first response may succeed while a redirect target or protected page fails.
Separate network reachability from rendering problems
If the exact entry URL returns an HTTP response from the renderer, the original TCP refusal may be resolved, but PDF generation can still fail later. CSS, images, JavaScript, and other assets make their own requests and can have different hostnames or authentication rules. Review wkhtmltopdf stderr and the resulting page behavior. KnpSnappyBundle documents limitations with modern JavaScript and ES6; those can affect rendering but do not, by themselves, explain a refused TCP connection to Symfony.
Check KnpSnappyBundle settings after the probe
Once network reachability is understood, verify that the bundle launches the intended executable and can create its intermediate files. KnpSnappyBundle documents the binary, temporary_folder, and process_timeout configuration options in its README. The temporary folder defaults to sys_get_temp_dir(); confirm the runtime user can write there if errors indicate a file or permission problem. Configure the binary path if the executable is not found or the wrong one is launched.
Adjust process_timeout only when logs indicate that the process exceeds its allowed time. A timeout is not the same as a connection refusal, and increasing it will not fix a wrong hostname or a closed port. The underlying Snappy package documentation on Packagist says it requires wkhtmltopdf 0.12.x; confirm compatibility with the executable installed in your image.
When rendering a page URL that uses relative assets, provide an absolute page URL so the browser engine has a base from which to resolve those paths. If the page itself is reachable but assets are not, make those asset URLs reachable from the renderer too.
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Avoid treating local-file access as a network fix
Do not enable --enable-local-file-access as a generic remedy for an HTTP connection failure. It changes access to local files; it does not repair Docker DNS, network membership, a listening port, or routing. The package documentation warns that local-file access can expose files and create remote-code-execution risks when processing untrusted HTML or JavaScript. Enable it only when local assets genuinely require it, and constrain the input and runtime accordingly. See the knp-snappy package documentation.
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If your task is to capture a clean website screenshot rather than to debug or generate a Symfony PDF, ScreenshotNeo provides a screenshot API and MCP server. It does not fix a Docker network path or replace a Symfony PDF workflow, but it can avoid running a browser renderer yourself for a screenshot. One GET request returns an image; for example, using the API’s documented request pattern:
curl -G "https://api.screenshotneo.com/v1/shot" -d access_key=YOUR_API_KEY --data-urlencode url=https://stripe.com -o shot.webpSee the ScreenshotNeo documentation for API options. It removes cookie and consent banners, newsletter popups, and chat widgets before capture, with each cleanup step configurable. Bot checks, blank pages, failed loads, timeouts, and cache hits are not billed. Its MCP server exposes take_screenshot, get_page_info, and capture_pdf for AI agents and MCP clients. The free plan includes 1,000 shots per month with no card; paid plans start at $5 for 3,000 shots. Sign up for the free plan.
Why the historical error report is not a Docker diagnosis
A wkhtmltopdf issue opened on December 9, 2016, records the literal ConnectionRefusedError wording in a Symfony 3 and KnpSnappyBundle report. The reporter described Windows Server 2008 R2, not Docker. That report can help identify the error string, but it does not establish the cause in a modern container layout or prove that localhost is the problem in every case. See wkhtmltopdf issue #3244.
Frequently Asked Questions
Does Symfony 7.4 change how Docker service names work?
No Symfony-specific setting changes Docker’s network addressing model; confirm the actual services, networks, and ports in your deployment.
Can I use an IP address instead of a Docker service name?
An IP can help isolate a DNS issue, but it may be unstable as containers are recreated and can bypass hostname-based routing. Prefer a resolvable service name on the shared network when that is your deployment’s design.
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