Deployment Maintenance Page

CEDAR cannot show an in-app modal while the Shiny process is restarting. During a container replacement, the browser is talking to nginx, not to the Shiny app, so friendly downtime messages have to come from nginx as static fallbacks.

CEDAR supports two separate proxy-level messages:

Mode	Marker	Use
Restarting	restarting.flag	Short GitHub deploy restart while the Shiny container is replaced and warmed.
Maintenance	maintenance.flag	Manual extended downtime for longer operational work.

Users who already have CEDAR open may see the in-app restart overlay from www/cedar-disconnect.js instead of the nginx static page. That overlay also reloads the page every 10 seconds, because Shiny websocket reconnects are not reliable after the backing container has been replaced.

The production deploy workflow supports the restart pattern:

1. Pull the new code.
2. Build the new Docker image while the old app continues serving users.
3. Write a short-lived restart marker file.
4. Replace the Shiny container.
5. Poll the local Shiny health check.
6. Remove the restart marker.

Files

The static page lives at:

deploy/nginx/cedar-restarting.html

The extended maintenance page lives at:

deploy/nginx/cedar-maintenance.html

The example nginx fragment lives at:

deploy/nginx/cedar-maintenance.conf.example

The default CI restart marker path is:

/var/www/cedar-maintenance/restarting.flag

Set the GitHub Actions secret CEDAR_RESTARTING_FLAG if the production server uses a different host-side marker path. If nginx runs in Docker, this must be the path on the host, not the path inside the nginx container.

Server Setup

On the production server, copy the static page to the directory nginx will read:

sudo mkdir -p /var/www/cedar-maintenance
sudo cp deploy/nginx/cedar-restarting.html /var/www/cedar-maintenance/cedar-restarting.html
sudo cp deploy/nginx/cedar-maintenance.html /var/www/cedar-maintenance/cedar-maintenance.html

Then adapt the nginx server block using deploy/nginx/cedar-maintenance.conf.example. The important pieces are:

• separate marker checks for maintenance.flag and restarting.flag
• maintenance taking precedence if both flags exist
• proxy_intercept_errors on; in the CEDAR proxy location
• Cache-Control: no-store so browsers do not keep downtime pages

After editing nginx:

sudo nginx -t
sudo systemctl reload nginx

Once this is installed, ordinary GitHub deploys should show the restart page only while CEDAR is actually being replaced and warmed. Extended maintenance is manual: create maintenance.flag to show the longer downtime page and remove it when CEDAR should be available again.