Make load balancers optional for MIGs #108
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Updates the write-metadata.sh script to write out the IATA code to /var/local/metadata
If M-Lab-managed VMs can use the Autojoin API to get a DNS entry, then they don't need a load balancer. Not only do load balancers turn out to be expensive, but they add additional complexity to the system. This commit adds the necessary changes to make load balancers optional.
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@stephen-soltesz: FYI, in case you see something that @robertodauria and I are not. It seems to WAI in with mlab-chs01 in sandbox. |
This is just to prepopulate the value explicitly, and in case Terraform would exit with an error if we are trying to check the value of a non-existent field.
VMs definitions that don't have a probability set explicitly will get the new default probability of 1.0.
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@robertodauria: After you reviewed this PR a week ago, I realized that I had forgot to add loadbalanced=(true|false) to the platform-cluster.tf files for mlab-staging and mlab-oti.
Additionally, @stephen-soltesz brought up a concern that there was a statically configured 1.0 probability for all VMs, which isn't how we run the production platform and isn't flexible enough. Since the probability feature was very much related to the intention of this PR, I went ahead and added a new feature to this PR which allows us to plumb probability from the TF configs through to the autonode-register container.
Since there are a fair number of changes since your last review, could I request that you take another look at this PR?
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Related to: m-lab/epoxy-images#277
We are experimenting with having VMs leverage the Autojoin API to get a DNS name, meaning that they will no longer need to be recorded in siteinfo. Additionally, this change obviates the need to load balance VMs, since each VM in an instance group will get its own DNS name and join the cluster independently.
This change adds a new "loadbalanced" field to the "migs" map which takes a boolean. For now, I'm just experimenting with "mlab1-chs0t", leaving the other sandbox VM loadbalanced.
All resources in the
loadbalancers.tffile now use a modifiedfor_eachloops, which eliminates MIG that have loadbalanced=false.Additionally, the change plumbs a new "loadbalanced" VM metadata attribute. The write-metadata.sh script on each machine that runs at boot will use the value of this to determine whether it needs to record the VM's external IPs or the external IPs of the load balancer.
This change is