addIoTDatabaseIndex races the IoT Agent and kills the services script

[kzangeli]

This repo's own CI hit it on 2026-09-19, in the Run Scorpio step of the PR check for #16:

MongoServerError: Collection iotagentjson.devices already exists.
Adding appropriate MongoDB indexes for IoT-Agent  ...
##[error]Process completed with exit code 1.

It is intermittent — the identical commit passed on re-run — so it shows up as a mystery red rather than as a bug.

The window

addIoTDatabaseIndex does:

db.getCollectionNames().forEach(c=>db[c].drop());
db.createCollection("devices");
...

By the time it runs, the IoT Agent container is already up and connected to the same database — it is started by the same docker compose up. If the agent creates devices between the drop loop and the createCollection call, the call fails.

On mongo 6.0, which is what MONGO_DB_VERSION pins, db.createCollection on an existing collection throws NamespaceExists; mongosh then exits 1; and services runs under set -e, so the whole invocation dies — after the stack is up, before the tutorial has run a single request.

(Worth knowing for later: mongo 8 made createCollection return {ok:1} in this case, so bumping MONGO_DB_VERSION would hide this rather than fix it.)

The fix

The two createCollection calls are redundant — createIndex creates the collection implicitly when it is missing. Dropping them closes the window with no other change.

Verified on mongo 6.0:

	current	amended
clean database	exit 0	exit 0
run twice in a row	exit 1	exit 0
collection created concurrently mid-script	exit 1	exit 0

and the resulting indexes are identical either way:

devices: {_id}, {_id.service,_id.id,_id.type}, {_id.type}, {_id.id}
groups:  {_id}, {_id.resource,_id.apikey,_id.service}, {_id.type}

Scope

Eight other tutorials carry the same function verbatim and are equally exposed: Big-Data-Spark, Concise-Format, IoT-Agent, IoT-Agent-JSON, IoT-Sensors, Short-Term-History, Subscriptions, Time-Series-Data. Happy to send the same one-hunk change to each if you would rather not sync it by hand — just say.

Independent of #16 — different file.

🤖 Generated with Claude Code

[jason-fox]

Fixed with a420da1