a year ago
Hello Railway Team,
I am writing to report a critical issue where my application's file writes are not being persisted to its mounted volume. All diagnostic tests performed from within the running application show success, but the files are immediately lost, indicating that writes are being directed to a temporary or ephemeral filesystem layer instead of the actual persistent volume.
---
### 1. The Environment
* **Service:** FastAPI application deployed on Railway.
* **Volume:** A persistent volume is correctly mounted at `/app/assets`.
* **Permissions:** The service is running with `RAILWAY_RUN_UID=0`. My Start Command also successfully runs `chown -R root:root /app/assets` before the application starts.
* **Start Command:**
```bash
chown -R root:root /app/assets && mkdir -p /app/assets/uploads ... && uvicorn app.main:app ...
```
---
### 2. The Core Problem: Contradictory Evidence
There is a clear contradiction between what my running application process sees and what is actually stored on the persistent volume.
**A. The Application Process View (From a Diagnostic Endpoint):**
My diagnostic endpoint performs a write, wait, and read test. The logs from this test show a complete success from the application's perspective:
--- Diagnostic Results ---
INFO: Process running as UID: 0
INFO: settings.ASSETS_DIR is configured as: /assets
INFO: Absolute path of ASSETS_DIR is: /assets
INFO: Directory '/assets' exists.
INFO: Contents of '/assets': ['uploads', 'results', 'frames', ...]
INFO: Successfully ensured test directory exists at: /assets/test_dir_from_web
INFO: Successfully wrote to test file: /assets/test_file_from_web.txt
INFO: Read test successful: File '/assets/test_file_from_web.txt' still exists after delay.
INFO: Content of test file: 'Hello from the web process.'
--- Diagnostic Results ---
This proves the running process, as `root`, has permission to create directories and write files within the `/assets` directory it sees.
**B. The Persistent Volume View (From the Railway File Browser):**
Despite the successful logs above, the file browser for my persistent volume shows that none of these write operations actually persisted.
* The `test_dir_from_web` directory is **not** present.
* The `test_file_from_web.txt` file is **not** present.
* When I upload an image to `/app/assets/uploads`, the application logs a successful write, but the file **never appears** in the volume.
---
### 3. Conclusion
This evidence leads to one conclusion: **My running `uvicorn` process is not writing to the persistent volume.** It is writing to a temporary, ephemeral filesystem overlay that is discarded after the request is complete.
This explains why:
- The application reports success (it wrote to the temporary layer).
- A subsequent `GET` request for the same file results in a `404 Not Found` (the file doesn't exist on the persistent layer that the server reads from).
Could you please investigate my service's container and volume configuration to determine why writes from the running application process are not being saved to the persistent volume?
7 Replies
a year ago
Hey there—this usually comes down to a simple mount-point mismatch between what your application thinks it’s writing to and where Railway actually mounted your volume.
What’s happening
- You’ve mounted your persistent volume at
/app/assets. - Your FastAPI app (and your diagnostics) are all targeting
/assets.
Because Docker’s overlay file system treats /assets as a normal ephemeral directory inside the container, any files you write there never touch the real volume at /app/assets.
How to fix it
- Align your paths
- Preferred: Change your
ASSETS_DIR(and any hard-coded paths) to/app/assets. - Alternative: If you really want to keep
/assets, go into Railway’s dashboard and remount the volume at/assetsinstead of/app/assets.
- Preferred: Change your
- Update your startup script
Make sure you
chownandmkdirthe same directory your app will use after the volume is mounted. For example, if you standardize on/app/assets, then:
chown -R root:root /app/assets
mkdir -p /app/assets/uploads /app/assets/results …
uvicorn app.main:app … - Verify inside the container Open a Railway Shell and run:
mount | grep assets
ls -ld /app/assets /assets You should see your volume mounted at /app/assets, and /assets should be just a normal (ephemeral) directory.
4. Test persistence
- Hit your diagnostic endpoint to write a test file.
- Refresh the Railway File Browser on
/app/assets—you should now see the file you just created.
Check:
- Is
ASSETS_DIRpointing to/app/assets? - Does your start command
chown/mkdirthat same path? - Does
mount | grep assetsconfirm the volume is at/app/assets? - After writing via your diagnostics, does the file show up in the File Browser?
Once your code and your volume agree on the mount path, your writes will persist—and you’ll stop seeing those phantom “success” messages from an ephemeral layer. Hope that helps!
a year ago
What is your mount path on your volume and what is your mount path in your service?
a year ago
They have to match otherwise you are not writing data. I think this is what the issue is
a year ago
If you do not know how to check it they have some documentation https://docs.railway.com/guides/volumes#using-the-volume
a year ago
You're exactly right—this is the issue.
When a volume is mounted at /app/assets, but the application (and all diagnostics) write to /assets, everything goes into an ephemeral layer and never reaches the actual volume.
Railway’s documentation on volumes specifically mentions:
"Your volume mount path must match the path your app writes to."
And because Nixpacks places the app in
/app, a relative path like./assetsactually resolves to/app/assets.
Aligning the two—by ensuring the application writes to /app/assets—resolves the issue and allows files to persist correctly.
mycodej
Hey there—this usually comes down to a simple mount-point mismatch between what your application thinks it’s writing to and where Railway actually mounted your volume. **What’s happening** * You’ve mounted your persistent volume at `/app/assets`. * Your FastAPI app (and your diagnostics) are all targeting `/assets`. Because Docker’s overlay file system treats `/assets` as a normal ephemeral directory inside the container, any files you write there never touch the real volume at `/app/assets`. **How to fix it** 1. **Align your paths** * **Preferred**: Change your `ASSETS_DIR` (and any hard-coded paths) to `/app/assets`. * **Alternative**: If you really want to keep `/assets`, go into Railway’s dashboard and remount the volume at `/assets` instead of `/app/assets`. 2. **Update your startup script** Make sure you `chown` and `mkdir` the _same_ directory your app will use _after_ the volume is mounted. For example, if you standardize on `/app/assets`, then: ```bash chown -R root:root /app/assets mkdir -p /app/assets/uploads /app/assets/results … uvicorn app.main:app … ``` 3. **Verify inside the container** Open a Railway Shell and run: ```bash mount | grep assets ls -ld /app/assets /assets ``` You should see your volume mounted at `/app/assets`, and `/assets` should be just a normal (ephemeral) directory. 4. **Test persistence** * Hit your diagnostic endpoint to write a test file. * Refresh the Railway File Browser on `/app/assets`—you should now see the file you just created. **Check:** * Is `ASSETS_DIR` pointing to `/app/assets`? * Does your start command `chown`/`mkdir` that same path? * Does `mount | grep assets` confirm the volume is at `/app/assets`? * After writing via your diagnostics, does the file show up in the File Browser? Once your code and your volume agree on the mount path, your writes will persist—and you’ll stop seeing those phantom “success” messages from an ephemeral layer. Hope that helps!
a year ago
You're right. It was just a simple misconfiguration. And i change the mount directory on the dockerfile side. Voila, work like magic.
Thanks for the response!
sim
What is your mount path on your volume and what is your mount path in your service?
a year ago
Already solved; thanks!
Status changed to Open brody • 11 months ago
Status changed to Solved brody • 11 months ago