Advice on using SNMP

A bit off topic, but I would be using node-red for collecting the data so maybe not too far off.
I have about a dozen assorted devices that I would like to monitor various aspects of and am wondering whether using SNMP would be a good route to go. Does anyone here have any views?

In an attempt to learn about it I have been following this tutorial (How To Install and Configure an SNMP Daemon and Client on Ubuntu 18.04 | DigitalOcean) using two Ubuntu 20.04 systems, one as manager and one as agent. All goes well until I try to change to password of the newly created demo user with the command (on the manager)

snmpusm -u demo -l authPriv -a MD5 -x DES -A temp_password -X temp_password agent_server_ip_address passwd temp_password new_password

with the appropriate IP for the agent machine. The response is

Error in packet.
Reason: wrongLength (The set value has an illegal length from what the agent expects)
Failed object: SNMP-USER-BASED-SM-MIB::usmUserOwnPrivKeyChange.".....)D.'..m`...."."demo"

In fact I get the same error with the original bootstrap user if I try
to change his pwd so there is something pretty basic wrong somewhere.
I have looked for alternative tutorials that might give a clue and
struggled through assorted man pages but can't work out what is going
wrong so if anyone has any ideas on this one then that would be great.

I can tell you that SNMP is great - when it works. Otherwise it is a right pain.

For example, some SNMP entries are represented by large numbers that JavaScript won't normally handle. Worse, some of those large numbers seem to be represented in a non-standard variable length byte format that I've not managed to work out how to interpret using the SNMP node in a flow.

However, SNMP is well supported by Telegraf if you are using that and there are even pre-canned Grafana dashboards for things like Synology NAS's and Ubiquity network kit.

Can't say that I've ever tried to use a custom SNMP service on an OS though so can't help there I'm afraid.

What are you looking to monitor? Again I've found Telegraf to be fantastic at monitoring Linux servers and it is trivial to feed its data into InfluxDB.

Pi and Ubuntu systems mainly. I have just started looking at Telegraf too, If I do go with SNMP would you suggest using Telegraf to get the data into Influx and not bother with putting node-red in the middle?

Now if I could just get SNMP going ....

Generally, yes, it seems a lot easier to me personally. Maybe check out some of the pre-canned Grafana dashboards as some of them have Telegraf configurations you can at least view to see how they are done - or just copy if you are lucky.

OK, thanks Julian. Since I am only using this on an internal network, and I just need read only access I have gone with SNMP v1 protocol for the moment, and that seems to be working ok.

Absolutely unrelated (only in as much as it is SNMP) does anyone have experience with SNMP docker images. There seem to be a lot and before I go on a voyage of discovery I thought I might ask. I am looking for a simple server that will capture SNMP traps from a number of internet (or vpn to be agreed) connected clients

apologies for the spam

No, sorry. Just to note that running SNMP over Internet really needs SNMP v3 and even then I'm not entirely convinced it would be especially secure as I'm not sure how well tested that scenario is?