Hello everybody.
Well, on the previously weeks, my team and me have been working with the IPAM and its python-sdk (https://github.com/solarwinds/orionsdk-python). We wrote an python script that will retrieve an free ip address from a SUBNET based on a given NETWORK_DISTRIBUTION.
An example for a call the python script is:
python free_ipaddress.py hostname1 --distribution NETWORK_DISTRIBUTION
So, basically our script works fine, our script workflow's is like following:
-> Query the database retrieve the FIRST free IP Address from a given subnet, marked as available based on its status
-> Mark the IP as reserved, changing the status value and registering the hostname of its record
-> And then print on stdout the IP and its record values as a JSON
How our workflow works is that the stdout generated by the IPAM python script is consumed by a tool called Terraform (a tool to provision and maintaining infrastructure as a code), and then the VM is deployed with IP Address generated and reserved on the IPAM.
The problem here is that when terraform (plans/apply) deploys multiple infra works on a way that sends the tasks to executes in background, by example, when I want to deploy and register 4 VMs on a same subnet, it will work mostly like execute a shell script like the following:
#!/bin/bash python free_ipaddress.py hostname1 --distribution NETWORK_DISTRIBUTION & python free_ipaddress.py hostname2 --distribution NETWORK_DISTRIBUTION & python free_ipaddress.py hostname3 --distribution NETWORK_DISTRIBUTION &
However, if you execute just one line or line by line of the script, both methods will work fine, since there will be a little time between each execution, even when you sends to execute to background the tasks, but it's not like that when you query to the DB at the same time. The multiple executions will retrieve the same IP, it happens because on the IPAM when the first line runs the second and the third runs as well at the same time, the multiple executions going to background and query the database at the same time, then the three scripts executes the same workflow, but since there's no be deference between each query, the SELECT statement will return the same row, since it's not yet update by any previously execution, and it's status is available. So, every execution takes the same row ID, and then this row is updated 3 times, one by each hostname.
SELECT TOP 1 I.IpNodeId, I.Status, I.DisplayName FROM IPAM.IPNode I WHERE Status=2 AND I.Subnet.DisplayName = 'SUBNET_NAME'
In this case the same IP (180.100.2.36) is taken and updated with the three hostnames three times.
If you instead of executing the previously shell script, executes one like the following, it will work fine because the queries to the table aren't executing parallelly, and there is time to update the status of the record, its going to register three different hostnames on a same subnet:
#!/bin/bash python free_ipaddress.py hostname1 --distribution NETWORK_DISTRIBUTION && python free_ipaddress.py hostname2 --distribution NETWORK_DISTRIBUTION && python free_ipaddress.py hostnam03 --distribution NETWORK_DISTRIBUTION &&
The previously works since &&: command after && is executed if, and only if, command before && returns an exit status of zero.
A workaround approach will be putting a random little sleep time inside of the python script, before the function call, something like:
time.sleep(random.random() * 10)
But I don’t know, this way doesn't like to me, there could be parallel executions if a user wants to register a bigger number of IPs, very minimal, but could by possible.
My point/question is, how to update the IPAM.IPNode table concurrently?
Any help? I will appreciate it, thanks in advance.