AEP Custom App questions?

[Ajay K]

Just wanted some clarifications around installing and running custom applications on the new AEP firmware.

1) With the new firmware, the custom app can be run from within the Conduit flash as opposed to setting up the custom app on the external mcard correct?

2) Is it possible to order when the custom app runs when the conduit boots up, for example, can it be run before the node-red application reboots or can it be parallelized to start with the lora wan server and/or mqtt broker?

3) If by any chance the Custom application exits because of an exception, what is the best way to restart it. Basically detect that it has exited and automatically restart it?

4) This is a nodejs based custom app, can the console.log statements being executed within the custom app be re-directed to a log file under /var/logs/app/<app-name>/<app-name>.log?

Thanks,
Ajay

[Jeff Hatch]

Ajay,

1) With the new firmware, the custom app can be run from within the Conduit flash as opposed to setting up the custom app on the external mcard correct?

Yes, that is correct, you will not need an SD card on AEP-1.4.1

2) Is it possible to order when the custom app runs when the conduit boots up, for example, can it be run before the node-red application reboots or can it be parallelized to start with the lora wan server and/or mqtt broker?

The custom app will be started just before the Node-RED app. Are you looking to restart the custom application in tandem with the Node-RED application? The LoRa network server starts before the custom application, but after mosquitto. The following is the contents of rc5.d:

admin@mtcdt:/etc/rc5.d# ls
S01networking                    S78ddns
S02dbus-1                        S80dnsmasq
S15mountnfs.sh                   S80lora-network-server
S20hostapd                       S81ppp
S20hwclock.sh                    S81time
S20ntpd                          S85ser-cli
S20syslog                        S85smsd
S30api                           S85wan-manager
S31local-time                    S90crond
S50usb-gadget                    S92led-cd-ss
S60lighttpd                      S95annex-client
S61syslog-configure              S95auto-reboot
S65remove-rs9113                 S95call_home
S70mosquitto                     S95customapp
S71backoff-timers                S95gps
S71database-init                 S95led-status_heartbeat_trigger
S71wireless-conf                 S95node-red
S72lanup                         S95remove_upgrade_occurred
S72post-upgrade                  S95reset-handler
S73bluetooth                     S95stunnel
S73wifi                          S95watchdogd
S75firewall                      S99rmnologin.sh
S75routing_table_setup           S99stop-bootlogd
S76sshd

3) If by any chance the Custom application exits because of an exception, what is the best way to restart it. Basically detect that it has exited and automatically restart it?

There are several ways to accomplish restart on a failure/fault/crash. One of the simplest it to write a script that is started by the applications Start script that does something like the following:

MYAPP="app_executable -arg1 -arg2 ..."
until $MYAPP; do
    echo "myapp exited with status $? -restarting..." >&2
    sleep 1
done

This will run the app executable, and when it exits will restart it. The only problem here is shutting down the app. For that you would need a signal handler to stop the executable app.

4) This is a nodejs based custom app, can the console.log statements being executed within the custom app be re-directed to a log file under /var/logs/app//.log?

You can do the same as what is done with Node-RED on the Conduit – pipe the output of the process to a file:

myapp -arg1 -arg1 >& /var/log/app//.log

Hope that helps,

Jeff

[Ajay K]

Hi Jeff,

Thanks for taking the time to respond and writing in such detail. In terms of restarting an application, do other apps like lora-wan server, and node-red, do they implement this at their end. I am just wondering if its worth spending time on this?

Also is there a way to invoke this script that you mentioned above from node-red flow to say re-start a custom app, if it went down by any chance?

Thanks,
Ajay

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