Tolerate deployment failures¶
When proceeding to large scale deployments, it happens very often to have infrastructure problems such as network outages, wrong configurations applied on hardware, hard drive issues, etc.
It is unpleasant to deploy hundred of nodes and only have a few of them which failed. On most of large-scale use-cases, deployers would not care about these nodes, as long as the cloud can already be used with the successfully deployed servers.
For that purpose, it is possible in TripleO to specify a percentage value, per role, that will tell how much failures we tolerate.
Example: We deploy 50 compute nodes with the role “Compute”. If I set the following environment, my deployment will go until the end even if up to 5 nodes fail to deploy:
parameter_defaults: ComputeMaxFailPercentage: 10
At the end of the deployment, a report will be printed and if nodes failed to deploy, it’ll be shown like this:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~~~~~~~~~~~~~~ State Information ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~~~~~~~~~ Number of nodes which did not deploy successfully: 3 ~~~~~~~~~~~~~~ This or these node(s) failed to deploy: compute3, compute24, compute29 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
If one or multiple node(s) failed to deploy, the tripleoclient return code won’t be 0 and an error will be printed with a Python trace. Very often the problem can be read from the Ansible logs by searching for the nodes which didn’t deploy successfully.
If you want to target all the compute nodes in our deployment and you have more than one role to deploy computes, then you’ll probably want to allocate one value per role and distribute it based on your expectations and needs.
For now, this only works for the execution of the deployment steps from config-download playbooks. Minor updates, major upgrades, fast forward upgrades and baremetal provisioning operations aren’t supported yet, but will certainly be in the future.