Using Azure IoT Edge, I have not found any way to guarantee the initialization order of containers/modules in a deployment. Suppose for example, I have 2 modules, A and B. A is a server and B is a client that depends on A. As far as I know, there's no way to guarantee that A starts up before B does.
The Azure IoT Edge deployment templates conform to the Docker Engine API, and I could not find any way to enforce dependencies through that API. As a workaround, I make no assumptions about which containers are running in each container's code. This works, although the overhead of additional code is not ideal, especially considering a tool like docker-compose would make enforcing initialization order rather trivial.
I want to do something like this (src: https://docs.docker.com/compose/compose-file/):
version: "3.7"
services:
web:
build: .
depends_on:
- db
- redis
redis:
image: redis
db:
image: postgres
As a workaround, and following the example above, in the web container I've been doing things like the following to ensure postgres is up and running before web performs postgres dependent actions:
postgresIsUp = False
while not postgresIsUp:
try:
pingPostgres()
postgresIsUp = True
except PingError:
print("postgres is not yet running")
This is, of course, a contrived example with obvious flaws, but it demonstrates the gist of the workaround.
