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MEP-12: Rack Spreading (#125)
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‎.gitignore

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.idea
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docs/build
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*.pdf

‎.vscode/settings.json

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‎docs/src/development/proposals/MEP12/README.md

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# Rack Spreading
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Currently, when creating a machine through the metal-api, the machine is placed randomly inside a partition. This algorithm does not consider spreading machines across different racks and different chassis. This may lead to the situation that a group of machines (that for example form a cluster) can end up being placed in the same rack and the same chassis.
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Spreading a group of machines across racks can enhance availability for scenarios like a rack loosing power or a chassis meltdown.
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So, instead of just randomly deciding the placement of a machine candidate, we want to propose a placement strategy that attempts to spread machine candidates across the racks inside a partition.
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## Placement Strategy
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Machines in the project are spread across all available racks evenly (best effort), the user can optionally pass placement tags which will be considered for spreading the machines as well (this will for example allow spreading by a cluster id tag inside the same project).
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## API
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```golang
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// service/v1/machine.go
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type MachineAllocation struct {
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// existing fields are omitted for readability
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PlacementTags []string `json:"tags" description:"by default machines are spread across the racks inside a partition for every project. if placement tags are provided, the machine candidate has an additional anti-affinity to other machines having the same tags"`
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}
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```

‎docs/src/development/proposals/MEP12/partitioning-1.svg

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‎docs/src/development/proposals/MEP12/partitioning-2.svg

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‎docs/src/development/proposals/MEP12/partitioning-3.svg

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‎docs/src/development/proposals/MEP12/partitioning.drawio.svg

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‎docs/src/development/proposals/MEP12/partitioning.md

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---
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marp: true
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theme: metal-stack
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paginate: true
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footer: Gerrit Schwerthelm – x-cellent technologies GmbH — metal-stack Training
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backgroundImage: url("https://metal-stack.io/images/shape/banner.png")
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---
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<!-- _class: cover lead -->
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![h:200px](https://metal-stack.io/images/metal-stack-full-white-border.svg)
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---
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<!-- _class: cover lead -->
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# Multi-Partition-Layout
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---
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<!--
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_class: lead
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_backgroundColor: #1f1f1f
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_backgroundImage:
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_footer: ""
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-->
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![bg contain](partitioning-1.svg)
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---
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<!--
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_class: lead
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_backgroundColor: #1f1f1f
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_backgroundImage:
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_footer: ""
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-->
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![bg contain](partitioning-2.svg)
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---
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<style>section { font-size: 30px; }</style>
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# Multi-Partition-Layout Properties
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- Fully independent locations with own storage and own node networks
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- Clusters can only be created independent in every location
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- Failover mechanism for deployed applications requires duplicated deployments, which can serve indepedently
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- Failover through BGP
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- If cluster nodes are spread across partitions (not implemented yet), nodes will not be able to reach each other
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- Would require an overlay network for inter-node-communication
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---
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<!-- _class: cover lead -->
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# Single-Partition-Layout
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---
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<!--
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_class: lead
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_backgroundColor: #1f1f1f
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_backgroundImage:
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_footer: ""
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-->
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![bg contain](partitioning-3.svg)
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---
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<style>section { font-size: 30px; }</style>
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# Single-Partition-Layout Properties
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- Multiple groups of racks at multiple locations but connected to same CLOS topology
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- All racks can connect to the same storage network
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- Nodes in private networks can communicate
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- When creating a cluster, nodes will be randomly spread across the racks
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- Possible improvement of this situation, see `MEP-12: Rack Spreading`
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---
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# MEP-12: Rack Spreading
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- Instead of selecting a machine from a machine pool randomly
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- Get all existing machines in the same project and count to which rack they belong
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- Place machine on the rack with the least amount of machines already allocated
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- Best effort only

‎docs/src/development/proposals/index.md

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Once a proposal was accepted, an issue should be raised and the implementation should be done in a separate PR.
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| Name | Description | State |
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| :----------------------- | :--------------------------------------------- | :-------------: |
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| [MEP-1](MEP1/README.md) | Distributed Control Plane Deployment | `In Discussion` |
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| [MEP-2](MEP2/README.md) | Two Factor Authentication | `Aborted` |
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| [MEP-3](MEP3/README.md) | Machine Re-Installation to preserve local data | `Completed` |
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| [MEP-4](MEP4/README.md) | Multi-tenancy for the metal-api | `Accepted` |
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| [MEP-5](MEP5/README.md) | Shared Networks | `Completed` |
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| [MEP-6](MEP6/README.md) | DMZ Networks | `Completed` |
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| [MEP-8](MEP8/README.md) | Configurable Filesystemlayout | `Completed` |
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| [MEP-9](MEP9/README.md) | No Open Ports To the Data Center | `In Progress` |
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| [MEP-11](MEP9/README.md) | Auditing of metal-stack resources | `In Progress` |
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| Name | Description | State |
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| :------------------------ | :--------------------------------------------- | :-------------: |
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| [MEP-1](MEP1/README.md) | Distributed Control Plane Deployment | `In Discussion` |
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| [MEP-2](MEP2/README.md) | Two Factor Authentication | `Aborted` |
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| [MEP-3](MEP3/README.md) | Machine Re-Installation to preserve local data | `Completed` |
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| [MEP-4](MEP4/README.md) | Multi-tenancy for the metal-api | `Accepted` |
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| [MEP-5](MEP5/README.md) | Shared Networks | `Completed` |
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| [MEP-6](MEP6/README.md) | DMZ Networks | `Completed` |
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| [MEP-8](MEP8/README.md) | Configurable Filesystemlayout | `Completed` |
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| [MEP-9](MEP9/README.md) | No Open Ports To the Data Center | `Completed` |
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| [MEP-11](MEP11/README.md) | Auditing of metal-stack resources | `Completed` |
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| [MEP-12](MEP12/README.md) | Rack Spreading | `In Discussion` |

‎marp/themes/metal-stack.css

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/* @theme metal-stack */
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@import url('https://fonts.googleapis.com/css2?family=Sorts+Mill+Goudy:ital@1&display=swap');
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color: white;
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background-image: url('https://metal-stack.io/images/background/banner-back.png') !important;
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section.cover footer {
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color: white;
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footer {
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text-align: center;
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font-family: "Sorts Mill Goudy";
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