Distribute dynamic IPs across subnets via dynamic_subnet_strategy - #2820
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WalkthroughAdds the Suggested reviewers: Priority: ➖ Normal Severity of issue fixed: Medium Merge Risk: ⚪ Minimal · up to The least-loaded strategy performs one initial count scan per network and maintains counts incrementally, so no concrete merge-blocking risk remains. 🚥 Pre-merge checks | ✅ 4 | ❌ 1❌ Failed checks (1 warning)
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Inline comments:
In
`@src/bosh-director/lib/bosh/director/deployment_plan/ip_provider/ip_provider.rb`:
- Line 165: Update the candidate-list shortcut in the relevant IP provider
method so it returns early only when candidates is empty; delegate every
non-empty list, including a single candidate, to LeastLoaded#order to preserve
nic_group co-location matching.
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jobs/director/specjobs/director/templates/director.yml.erbsrc/bosh-director/lib/bosh/director/config.rbsrc/bosh-director/lib/bosh/director/deployment_plan.rbsrc/bosh-director/lib/bosh/director/deployment_plan/ip_provider/ip_provider.rbsrc/bosh-director/lib/bosh/director/deployment_plan/subnet_distribution.rbsrc/bosh-director/lib/bosh/director/deployment_plan/subnet_distribution/first_fit.rbsrc/bosh-director/lib/bosh/director/deployment_plan/subnet_distribution/least_loaded.rbsrc/bosh-director/spec/unit/bosh/director/config_spec.rbsrc/bosh-director/spec/unit/bosh/director/deployment_plan/ip_provider/ip_provider_spec.rbsrc/bosh-director/spec/unit/bosh/director/deployment_plan/subnet_distribution/first_fit_spec.rbsrc/bosh-director/spec/unit/bosh/director/deployment_plan/subnet_distribution/least_loaded_spec.rbsrc/bosh-director/spec/unit/bosh/director/deployment_plan/subnet_distribution_spec.rb
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Inline comments:
In
`@src/bosh-director/lib/bosh/director/deployment_plan/subnet_distribution/least_loaded.rb`:
- Line 96: Update the LeastLoaded#order balancing path and
dynamic_ip_counts_by_subnet flow to avoid rescanning all dynamic
Models::IpAddress records for each allocation in a batch. Compute subnet counts
once, then increment the relevant count after each successful dynamic
reservation while preserving the existing candidate-subnet range rules;
alternatively, replace the per-address scan with an equivalent database
aggregation.
- Line 77: Update LeastLoaded#nic_group_leader_cloud_properties so its sibling
IP reservation query matches both static and dynamic rows for the same
instance_id and nic_group; remove the static-only filtering while preserving the
existing subnet selection behavior.
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spec/director.yml.erb_spec.rbsrc/bosh-director/lib/bosh/director/deployment_plan/ip_provider/ip_provider.rbsrc/bosh-director/lib/bosh/director/deployment_plan/subnet_distribution/least_loaded.rb
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Inline comments:
In
`@src/bosh-director/lib/bosh/director/deployment_plan/ip_provider/ip_provider.rb`:
- Around line 24-26: Update IpProvider#release so
`@subnet_strategy.record_release` is invoked only for dynamic reservations,
preserving the existing ManualNetwork subnet lookup for eligible releases while
excluding static manual reservations from strategy count updates.
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src/bosh-director/lib/bosh/director/deployment_plan/ip_provider/ip_provider.rbsrc/bosh-director/lib/bosh/director/deployment_plan/subnet_distribution/first_fit.rbsrc/bosh-director/lib/bosh/director/deployment_plan/subnet_distribution/least_loaded.rbsrc/bosh-director/spec/unit/bosh/director/deployment_plan/ip_provider/ip_provider_spec.rbsrc/bosh-director/spec/unit/bosh/director/deployment_plan/subnet_distribution/first_fit_spec.rbsrc/bosh-director/spec/unit/bosh/director/deployment_plan/subnet_distribution/least_loaded_spec.rb
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…rategy
Add a director-wide strategy for placing auto-allocated (dynamic) IPs
across the subnets of a manual network within an AZ, replacing the
previous fill-first-only behavior.
New property `director.dynamic_subnet_strategy` (string enum, default
`first_fit`), implemented with the strategy pattern under
DeploymentPlan::SubnetDistribution:
- first_fit (default): unchanged legacy behavior; fill each subnet in
manifest order before spilling to the next.
- least_loaded: place new VMs in the least-loaded subnet of their AZ
so instances spread evenly, with nic_group follow-the-leader
co-location so all networks sharing an ENI (IPv4 + IPv6-single +
IPv6-prefix) land on the same subnet per instance. When a
same-nic_group sibling is already placed but no candidate subnet
mirrors its cloud_properties, the strategy fails loud
(NetworkReservationError) rather than scattering the ENI's addresses
across subnets (which the IaaS rejects at create_vm time).
IpProvider selects the strategy from Config and delegates subnet
ordering to it via #subnets_in_allocation_order (the order is
strategy-defined, not necessarily fill-first). SubnetDistribution.build
owns the allowed set and is the single point that enforces it: an
unknown value fails loud with ValidationInvalidValue (nil selects the
default), so a misconfigured director surfaces a clear error on its
first deployment, consistent with how UpdateConfig validates
default_update_vm_strategy at point-of-use rather than in Config. Job
spec and director.yml.erb expose the property with first_fit default.
Covered by unit specs for each strategy, the selector/factory (incl.
invalid-value rejection), the Config accessor, and IpProvider
delegation.
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What is this change about?
Implements the even-distribution requested in #2622: when an AZ has more than one subnet on a manual network, spread auto-allocated (dynamic) IPs across those subnets instead of filling the first before using the next.
Adds
director.dynamic_subnet_strategy(defaultfirst_fit):first_fit(default): unchanged legacy behavior.least_loaded: place each new VM in the least-loaded subnet of its AZ, with nic_group follow-the-leader co-location so all networks sharing an ENI land on the same subnet.Implemented as a strategy under
DeploymentPlan::SubnetDistribution;IpProviderselects the strategy and delegates subnet ordering.least_loadedcaches per-subnet counts per deploy (seeded lazily, kept current on allocate/release) so balancing stays O(1) per reservation.Please provide contextual information.
Closes #2622. No related PRs or discussions.
What tests have you run against this PR?
config_spec,subnet_distribution+first_fit+least_loadedspecs, the fullip_providerspec directory.spec/director.yml.erb_spec.rb.rubocopon all changed files.How should this change be described in bosh release notes?
The director can now distribute auto-allocated (dynamic) IPs evenly across multiple subnets within an AZ via the new opt-in
director.dynamic_subnet_strategyproperty (least_loaded). The default (first_fit) preserves existing behavior.Does this PR introduce a breaking change?
No. The default
first_fitis byte-for-byte the previous behavior;least_loadedis opt-in.Tag your pair, your PM, and/or team!
AI Review Feedback
All CodeRabbit comments addressed: single-candidate co-location bypass, static-sibling co-location, static-release count guard, and the least_loaded performance (per-deploy count caching); docstring coverage and this description updated.