Improve docs about camera device names

docs/config.for.camera.usb.md

@@ -37,6 +37,9 @@ For more details about formats it is better to use
 
 Next, [test config](./test.config.md).
 
+Note: if you have more cameras you probably want to use device by-id or by-path,
+see [tuning](./configuration.tuning.md) for more details.
+
 ## Real world example
 
 Raspberry Pi Zero W with endoscope camera over USB, registered as `/dev/video1`:

docs/configuration.env.full.md

@@ -9,7 +9,7 @@ Config for camera is to the script as environment variables (env vars).
 * `PRINTER_ADDRESS` - Printer address to ping, if address is unreachable there
   is no point in sending an image. Set to `127.0.0.1` to always send images.
   Set to empty value to disable ping check and always send images.
-  Default value `127.0.0.1`
+  Default value `127.0.0.1`.
 
 * `PRUSA_CONNECT_CAMERA_TOKEN` - required, PrusaConnect API key
 
@@ -22,6 +22,8 @@ Config for camera is to the script as environment variables (env vars).
 * `CAMERA_DEVICE` - camera device to use, if you use Raspberry Pi camera
   attached to the CSI via camera ribbon then leave as is
   Default `/dev/video0` which points to first detected camera.
+  If you have more cameras you probably want to use device
+  by-id or by-path, see [tuning](./configuration.tuning.md) for more details.
 
 * `CAMERA_SETUP_COMMAND` - camera setup command and params executed before
   taking image, default value is empty, because some cameras do not support it,

docs/configuration.tuning.md

@@ -7,6 +7,51 @@ Below steps depend on the camera capabilities, thus your mileage may vary.
 Notice that Prusa Connect has file size limit something about 8MB of the image uploaded,
 so there may be no point in getting images with super high resolutions.
 
+## Using predicable camera device names
+
+Somethimes devices change their id so once given camera is under `/dev/video1`
+while another restart and it is under `/dev/video2` and swaps with another one.
+
+If you want to have a predictable camera identifiers then see directory
+`/dev/v4l/by-id` or `/dev/v4l/by-path` and choose the one that you prefer
+
+Example on Rasberry Pi with CSI camera and two USB cameras:
+
+```text
+pi@hormex:~ $ tree /dev/v4l
+/dev/v4l
+├── by-id
+│   ├── usb-Generic_USB_Camera_200901010001-video-index0 -> ../../video3
+│   ├── usb-Generic_USB_Camera_200901010001-video-index1 -> ../../video4
+│   ├── usb-Microsoft_Microsoft®_LifeCam_HD-3000-video-index0 -> ../../video1
+│   └── usb-Microsoft_Microsoft®_LifeCam_HD-3000-video-index1 -> ../../video2
+└── by-path
+    ├── platform-bcm2835-codec-video-index0 -> ../../video18
+    ├── platform-bcm2835-isp-video-index0 -> ../../video20
+    ├── platform-bcm2835-isp-video-index1 -> ../../video21
+    ├── platform-bcm2835-isp-video-index2 -> ../../video22
+    ├── platform-bcm2835-isp-video-index3 -> ../../video23
+    ├── platform-fd500000.pcie-pci-0000:01:00.0-usb-0:1.3:1.0-video-index0 -> ../../video3
+    ├── platform-fd500000.pcie-pci-0000:01:00.0-usb-0:1.3:1.0-video-index1 -> ../../video4
+    ├── platform-fd500000.pcie-pci-0000:01:00.0-usb-0:1.4:1.0-video-index0 -> ../../video1
+    ├── platform-fd500000.pcie-pci-0000:01:00.0-usb-0:1.4:1.0-video-index1 -> ../../video2
+    ├── platform-fe801000.csi-video-index0 -> ../../video0
+    └── platform-feb10000.codec-video-index0 -> ../../video19
+```
+
+so now if I want to have a Camera-1 always to point to the LifeCam_HD-3000
+I can use:
+
+```shell
+CAMERA_DEVICE=/dev/v4l/by-id/usb-Microsoft_Microsoft®_LifeCam_HD-3000-video-index0
+```
+
+and for CSI camera (notice it is not available under `by-id`):
+
+```shell
+CAMERA_DEVICE=/dev/v4l/by-path/platform-fe801000.csi-video-index0
+```
+
 ## Getting higher quality camera images
 
 Use `v4l2-ctl` to get the list of available resolutions that camera provides

docs/service.kubernetes.md

@@ -18,6 +18,9 @@ for the content you can use with a [kustomize](https://kustomize.io/).
 
 - deployment possible using for example kustomize
 
+- camera device - if you have more cameras you probably want to use device
+  by-id or by-path, see [tuning](./configuration.tuning.md) for more details
+
 ## Examples
 
 - [deployment-1.yaml](https://github.com/nvtkaszpir/prusa-connect-camera-script/blob/master/k8s/deployment-1.yaml)