travis_farmer:
course, if the server is down, it is likely so is the PHP source
I did assume "radio server" and "web server" are wrapped in different containers (e.g. different computers).
and to limit issues, perhaps i will just limit posting the dynamic image to when i want to alert that the radio station is on-air.
The usual strategy when such things are a concern is to have a separate thread of execution (e.g. dedicated daemon or something in your radio server) that outputs (copies / links / moves) a static image based on the current status. The web server serves the static image with a no-cache or short-time-cache setting. Doing that breaks the interconnect between the two servers.
And, if you REALLY want to get fancy check the image timestamp in your PHP code. If the image is older than expected serve a "the whole freaking mess is dead" static image.
Another option is to put a database (ideally on the same hardware as the web server) between the status-checker and the web server. The status-checker updates a database record based on the radio server's status. The web server queries the database server for the current status then serves a static image based on that status. As an added bonus you can log up-time and other information in the same database.