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<@ULVA73B9P> I'm using LocalForward 14200 localhos...
# ask-marvin
l
@Marvin I'm using LocalForward 14200 localhost:4200 in my configured SSH host so I can access the GUI of my server's prefect. I'm running the prefect API on my local as well on the 4200, that's why I use a different port (14200). When I go to localhost:14200 I see exactly the same deployments and runs from my local. To confirm, I stopped the prefect-server and prefect-worker containers and localhost:14200 just shows a gray screen because it's actually trying to connect to my local localhost:4200 API instead of the remote. How to fix it?
m
✅ thought for 138.9 seconds
What’s happening is that the UI is being told to use 
localhost:4200
as its API URL, so when you open the forwarded UI on 
localhost:14200
, the browser then makes API calls to your own machine’s 
localhost:4200
. Fix: configure the remote Prefect server to advertise the correct API URL to the UI. What to set on the remote server Set:
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bash
PREFECT_UI_API_URL=<http://localhost:14200/api>
Then restart the remote Prefect server. If you’re using Docker Compose, that would look something like:
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yaml
environment:
  PREFECT_UI_API_URL: <http://localhost:14200/api>
Why this works: - you open the UI at 
<http://localhost:14200>
- that request is SSH-forwarded to the remote server - the UI asks the server for 
/ui-settings
- the remote server responds with the configured 
api_url
- if that 
api_url
is 
<http://localhost:14200/api>
, your browser will send API requests through the same SSH tunnel instead of to your local Prefect instance on 
4200
Important note - 
localhost
in 
PREFECT_UI_API_URL
is interpreted by the browser, not the remote machine - so in your case, 
<http://localhost:14200/api>
is exactly what you want How to verify From your local machine:
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bash
curl <http://localhost:14200/ui-settings>
You should see JSON with:
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json
{
  "api_url": "<http://localhost:14200/api>"
}
If it still says 
<http://localhost:4200/api>
, the remote server is still advertising the wrong value. If you use a config file instead of env vars In 
prefect.toml
on the remote server:
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toml
[server.ui]
api_url = "<http://localhost:14200/api>"
Then restart the server. Related settings - 
PREFECT_UI_API_URL
/ `PREFECT_SERVER_UI_API_URL`: explicit UI API URL - if unset, Prefect may fall back to 
PREFECT_API_URL
or server host/port defaults, which often end up as 
<http://localhost:4200/api>
Docs/settings references: - Prefect server guide - Settings reference If you want, I can help you write the exact 
docker-compose.yml
change for your current Prefect server container.
l
@Marvin I have this in a .env: 
PREFECT_API_URL=<http://127.0.0.1:4200/api>
Could I keep it the same and just add a new
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PREFECT_UI_API_URL=<http://localhost:14200/api>
? Would it still work?
m
✅ thought for 15.1 seconds
Yes — that can work, with one important distinction: - 
PREFECT_API_URL
is used by Prefect clients/workers/CLI - 
PREFECT_UI_API_URL
is what the browser UI uses So you can keep:
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bash
PREFECT_API_URL=<http://127.0.0.1:4200/api>
and add:
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PREFECT_UI_API_URL=<http://localhost:14200/api>
That means: - processes running on the remote server still talk to the API at 
127.0.0.1:4200
- your browser visiting the forwarded UI at 
localhost:14200
will call the API through the SSH tunnel at 
localhost:14200/api
That’s actually a good setup for your use case. A couple of cautions: 1. Don’t include angle brackets in the actual 
.env
Use:
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bash
PREFECT_API_URL=<http://127.0.0.1:4200/api>
PREFECT_UI_API_URL=<http://localhost:14200/api>
not:
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bash
PREFECT_API_URL=<http://127.0.0.1:4200/api>
2. Set 
PREFECT_UI_API_URL
on the remote server container/process It needs to be available to the Prefect server that serves the UI. 3. Restart the server after changing it 4. Verify with:
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bash
curl <http://localhost:14200/ui-settings>
You should see:
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json
{
  "api_url": "<http://localhost:14200/api>"
}
If you want, paste your Compose service/env block and I’ll sanity-check exactly where those vars should go.
l
@Marvin I followed the steps and changed the forward to 
LocalForward 14200 localhost:14200
When I go to http://localhost:14200/dashboard I see a gray screen. This: http://localhost:14200/ui-settings returns a 
ERR_CONNECTION_RESET
.
m
✅ thought for 10.9 seconds
That change is the problem. 
LocalForward 14200 localhost:14200
means: - local port 
14200
- forwarded to remote 
localhost:14200
But your Prefect server is listening on remote 
4200
, not 
14200
. So the tunnel is now pointing at the wrong remote port, which explains: - gray screen - 
/ui-settings
connection reset What you want instead Keep the SSH forward as:
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ssh-config
LocalForward 14200 localhost:4200
That means: - local 
localhost:14200
-> remote 
localhost:4200
Then on the remote Prefect server, set:
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bash
PREFECT_API_URL=<http://127.0.0.1:4200/api>
PREFECT_UI_API_URL=<http://localhost:14200/api>
This is correct because: - remote server processes use 
127.0.0.1:4200
- your local browser uses 
localhost:14200
Why 
PREFECT_UI_API_URL=<http://localhost:14200/api>
is okay Even though it’s configured on the remote server, that value is consumed by the browser, so 
localhost:14200
refers to your local machine, which is exactly where the SSH tunnel is listening. Recommended setup SSH config:
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ssh-config
Host my-prefect-server
  HostName <http://your.server.com|your.server.com>
  User your-user
  LocalForward 14200 localhost:4200
Remote `.env`:
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bash
PREFECT_API_URL=<http://127.0.0.1:4200/api>
PREFECT_UI_API_URL=<http://localhost:14200/api>
Then restart the remote Prefect server container/process. Checks to run 1. On the remote machine, confirm Prefect is actually listening on 4200:
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curl <http://127.0.0.1:4200/api/health>
2. On your local machine, after reconnecting SSH:
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curl <http://localhost:14200/ui-settings>
You should get JSON back. 3. Also test:
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curl <http://localhost:14200/api/health>
If that works, the tunnel is good. One subtle issue to watch for If the UI loads from 
localhost:14200
and then calls 
<http://localhost:14200/api>
, that should work fine through the same tunnel. If it still doesn’t, the server may not have picked up 
PREFECT_UI_API_URL
, or there may be a browser cache issue. A hard refresh/incognito window can help. If you want, I can help you debug this step-by-step from: - your SSH config - your docker compose ports/env - the output of 
curl <http://127.0.0.1:4200/api/health>
on the remote - the output of 
curl <http://localhost:14200/ui-settings>
locally
l
@Marvin curl http://127.0.0.1:4200/ui-settings {"api_url":"http://127.0.0.1:4200/api","csrf_enabled":false,"auth":null,"flags":[]}*%* As you can see, it's still pointing to the local 4200, not the remote.
m
✅ thought for 11.5 seconds
127.0.0.1:4200
there is the remote server’s loopback, because you ran the 
curl
on the remote host. So that output alone does not mean it’s pointing at your laptop. The real issue is that your server has not picked up 
PREFECT_UI_API_URL
, because 
/ui-settings
is still advertising:
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json
"api_url":"<http://127.0.0.1:4200/api>"
It should instead advertise:
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json
"api_url":"<http://localhost:14200/api>"
Also: your output shows angle brackets in the URL:
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json
"<http://127.0.0.1:4200/api>"
Actually your pasted command/output suggests you may literally have values like:
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bash
PREFECT_API_URL=<http://127.0.0.1:4200/api>
PREFECT_UI_API_URL=<http://localhost:14200/api>
If so, that is wrong for 
.env
files. The values must be plain URLs, no 
< >
. Use exactly:
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bash
PREFECT_API_URL=<http://127.0.0.1:4200/api>
PREFECT_UI_API_URL=<http://localhost:14200/api>
Next steps 1. Fix the 
.env
values to remove angle brackets. 2. Make sure the vars are applied to the Prefect server container/process, not just somewhere else. 3. Restart/recreate the server container, not just the worker. For Docker Compose, usually:
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docker compose up -d --force-recreate prefect-server
or if service names differ, recreate the service that serves the API/UI. 4. Re-check on the remote host:
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curl <http://127.0.0.1:4200/ui-settings>
You want:
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json
{"api_url":"<http://localhost:14200/api>", ...}
Important detail If this is a containerized setup, editing a host 
.env
file is only useful if that file is actually referenced by the container via: - 
env_file:
- variable substitution in 
docker-compose.yml
- or exported into the process environment before startup So also inspect the running container env. For example:
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docker inspect <prefect-server-container> --format '{{range .Config.Env}}{{println .}}{{end}}' | grep PREFECT
You should see:
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bash
PREFECT_UI_API_URL=<http://localhost:14200/api>
If you don’t, the server container never received it. Likely diagnosis Most likely one of these is true: - 
PREFECT_UI_API_URL
is not actually set in the server container - the container wasn’t recreated after changing 
.env
- the 
.env
contains invalid bracketed values like 
<http://...>
If you paste your 
docker-compose.yml
service for Prefect server, I can tell you exactly where the variable needs to go.
l
@Marvin 
PREFECT_UI_API_URL
is not actually set in the server container. I added to the 
.env
file only. It should be taken because I do this on the 
prefect-server
container yaml:
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env_file:
      - .env
m
✅ thought for 13.3 seconds
If 
docker inspect
shows 
PREFECT_UI_API_URL
is not in the running 
prefect-server
container, then the container did not get that variable, even if 
env_file: .env
is in the Compose YAML. Most likely causes: 1. the container was not recreated after the 
.env
change 2. the wrong 
.env
file is being loaded 3. the variable is malformed in 
.env
4. the service you’re checking is not actually the one serving Prefect UI/API First: make sure the 
.env
line is exactly this
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bash
PREFECT_UI_API_URL=<http://localhost:14200/api>
No quotes needed, and no angle brackets. Then recreate the service, not just restart it:
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docker compose up -d --force-recreate prefect-server
A plain restart often won’t refresh env from 
env_file
. Then check again:
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docker inspect <prefect-server-container> --format '{{range .Config.Env}}{{println .}}{{end}}' | grep PREFECT_UI_API_URL
You should see:
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bash
PREFECT_UI_API_URL=<http://localhost:14200/api>
If you still don’t see it, verify Compose is reading the file you think it is:
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docker compose config
That shows the fully rendered config. Confirm: - the 
prefect-server
service has 
env_file:
- it points to the correct path - there isn’t another compose file overriding it You can also inspect the rendered env section more directly with:
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bash
docker compose config | sed -n '/prefect-server:/,/^[^[:space:]]/p'
Another subtle but important distinction Docker Compose has: - project-level 
.env
for variable substitution in compose files - 
env_file:
for injecting env vars into the container These are related but not the same thing. In your case, since you explicitly use:
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yaml
env_file:
  - .env
the file should be injected into the container if the service is recreated. Quick sanity test Temporarily add something obvious to `.env`:
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bash
FOO_TEST=hello
Recreate:
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docker compose up -d --force-recreate prefect-server
Then inspect:
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docker inspect <prefect-server-container> --format '{{range .Config.Env}}{{println .}}{{end}}' | grep FOO_TEST
- if it appears, your 
env_file
is working and the issue is specific to the Prefect var/value - if it does not appear, the service is not using the 
env_file
you think it is After it is present in the container, verify:
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bash
curl <http://127.0.0.1:4200/ui-settings>
Expected:
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json
{"api_url":"<http://localhost:14200/api>", ...}
Then locally, with SSH forward set back to:
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ssh-config
LocalForward 14200 localhost:4200
test:
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bash
curl <http://localhost:14200/ui-settings>
curl <http://localhost:14200/api/health>
If you want, paste: - the 
prefect-server
section of your 
docker-compose.yml
- the exact 
.env
lines for the two Prefect vars - the output of 
docker compose config | sed -n '/prefect-server:/,/^[^[:space:]]/p'
and I’ll pinpoint what’s wrong.
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