diff --git a/packages/xo-server-load-balancer/.editorconfig b/packages/xo-server-load-balancer/.editorconfig
new file mode 100644
index 000000000..b6db0112a
--- /dev/null
+++ b/packages/xo-server-load-balancer/.editorconfig
@@ -0,0 +1,65 @@
+# http://EditorConfig.org
+#
+# Julien Fontanet's configuration
+# https://gist.github.com/julien-f/8096213
+
+# Top-most EditorConfig file.
+root = true
+
+# Common config.
+[*]
+charset = utf-8
+end_of_line = lf
+insert_final_newline = true
+trim_trailing_whitespaces = true
+
+# CoffeeScript
+#
+# https://github.com/polarmobile/coffeescript-style-guide/blob/master/README.md
+[*.{,lit}coffee]
+indent_size = 2
+indent_style = space
+
+# Markdown
+[*.{md,mdwn,mdown,markdown}]
+indent_size = 4
+indent_style = space
+
+# Package.json
+#
+# This indentation style is the one used by npm.
+[/package.json]
+indent_size = 2
+indent_style = space
+
+# Jade
+[*.jade]
+indent_size = 2
+indent_style = space
+
+# JavaScript
+#
+# Two spaces seems to be the standard most common style, at least in
+# Node.js (http://nodeguide.com/style.html#tabs-vs-spaces).
+[*.{js,jsx,ts,tsx}]
+indent_size = 2
+indent_style = space
+
+# Less
+[*.less]
+indent_size = 2
+indent_style = space
+
+# Sass
+#
+# Style used for http://libsass.com
+[*.s[ac]ss]
+indent_size = 2
+indent_style = space
+
+# YAML
+#
+# Only spaces are allowed.
+[*.yaml]
+indent_size = 2
+indent_style = space
diff --git a/packages/xo-server-load-balancer/.gitignore b/packages/xo-server-load-balancer/.gitignore
new file mode 100644
index 000000000..fa69f37f1
--- /dev/null
+++ b/packages/xo-server-load-balancer/.gitignore
@@ -0,0 +1,5 @@
+/dist/
+/node_modules/
+
+npm-debug.log
+npm-debug.log.*
diff --git a/packages/xo-server-load-balancer/.npmignore b/packages/xo-server-load-balancer/.npmignore
new file mode 100644
index 000000000..c31ee82cb
--- /dev/null
+++ b/packages/xo-server-load-balancer/.npmignore
@@ -0,0 +1,10 @@
+/examples/
+example.js
+example.js.map
+*.example.js
+*.example.js.map
+
+/test/
+/tests/
+*.spec.js
+*.spec.js.map
diff --git a/packages/xo-server-load-balancer/.travis.yml b/packages/xo-server-load-balancer/.travis.yml
new file mode 100644
index 000000000..fb5d91729
--- /dev/null
+++ b/packages/xo-server-load-balancer/.travis.yml
@@ -0,0 +1,8 @@
+language: node_js
+node_js:
+  - 'stable'
+  - '4'
+
+# Use containers.
+# http://docs.travis-ci.com/user/workers/container-based-infrastructure/
+sudo: false
diff --git a/packages/xo-server-load-balancer/README.md b/packages/xo-server-load-balancer/README.md
new file mode 100644
index 000000000..89d9e1fd7
--- /dev/null
+++ b/packages/xo-server-load-balancer/README.md
@@ -0,0 +1,53 @@
+# xo-server-load-balancer [![Build Status](https://travis-ci.org/vatesfr/xo-server-load-balancer.png?branch=master)](https://travis-ci.org/vatesfr/xo-server-load-balancer)
+
+XO-Server plugin that allows load balancing.
+
+## Install
+
+Go inside your `xo-server` folder and install it:
+
+```
+> npm install --global xo-server-load-balancer
+```
+
+## Usage
+
+Like all other xo-server plugins, it can be configured directly via
+the web iterface, see [the plugin documentation](https://xen-orchestra.com/docs/plugins.html).
+
+## Development
+
+### Installing dependencies
+
+```
+> npm install
+```
+
+### Compilation
+
+The sources files are watched and automatically recompiled on changes.
+
+```
+> npm run dev
+```
+
+### Tests
+
+```
+> npm run test-dev
+```
+
+## Contributions
+
+Contributions are *very* welcomed, either on the documentation or on
+the code.
+
+You may:
+
+- report any [issue](https://github.com/vatesfr/xo-server-load-balancer/issues)
+  you've encountered;
+- fork and create a pull request.
+
+## License
+
+AGPL3 © [Vates SAS](http://vates.fr)
diff --git a/packages/xo-server-load-balancer/package.json b/packages/xo-server-load-balancer/package.json
new file mode 100644
index 000000000..ceb2aa763
--- /dev/null
+++ b/packages/xo-server-load-balancer/package.json
@@ -0,0 +1,78 @@
+{
+  "name": "xo-server-load-balancer",
+  "version": "0.3.1",
+  "license": "AGPL-3.0",
+  "description": "Load balancer for XO-Server",
+  "keywords": [
+    "load",
+    "balancer",
+    "server",
+    "pool",
+    "host"
+  ],
+  "homepage": "https://github.com/vatesfr/xo-server-load-balancer",
+  "bugs": "https://github.com/vatesfr/xo-server-load-balancer/issues",
+  "repository": {
+    "type": "git",
+    "url": "https://github.com/vatesfr/xo-server-load-balancer"
+  },
+  "author": {
+    "name": "Julien Fontanet",
+    "email": "julien.fontanet@isonoe.net"
+  },
+  "preferGlobal": false,
+  "main": "dist/",
+  "bin": {},
+  "files": [
+    "dist/"
+  ],
+  "engines": {
+    "node": ">=4"
+  },
+  "dependencies": {
+    "babel-runtime": "^6.11.6",
+    "cron": "^1.1.0",
+    "event-to-promise": "^0.7.0",
+    "lodash": "^4.16.2"
+  },
+  "devDependencies": {
+    "babel-cli": "^6.16.0",
+    "babel-eslint": "^7.0.0",
+    "babel-plugin-lodash": "^3.2.9",
+    "babel-plugin-transform-runtime": "^6.15.0",
+    "babel-preset-es2015": "^6.16.0",
+    "babel-preset-stage-0": "^6.16.0",
+    "dependency-check": "^2.5.1",
+    "ghooks": "^1.3.2",
+    "standard": "^8.2.0"
+  },
+  "scripts": {
+    "build": "NODE_ENV=production babel --source-maps --out-dir=dist/ src/",
+    "depcheck": "dependency-check ./package.json",
+    "dev": "NODE_DEV=development babel --watch --source-maps --out-dir=dist/ src/",
+    "lint": "standard",
+    "posttest": "npm run lint && npm run depcheck",
+    "prepublish": "npm run build"
+  },
+  "babel": {
+    "plugins": [
+      "transform-runtime",
+      "lodash"
+    ],
+    "presets": [
+      "es2015",
+      "stage-0"
+    ]
+  },
+  "standard": {
+    "ignore": [
+      "dist"
+    ],
+    "parser": "babel-eslint"
+  },
+  "config": {
+    "ghooks": {
+      "commit-msg": "npm test"
+    }
+  }
+}
diff --git a/packages/xo-server-load-balancer/src/density-plan.js b/packages/xo-server-load-balancer/src/density-plan.js
new file mode 100644
index 000000000..b407d7547
--- /dev/null
+++ b/packages/xo-server-load-balancer/src/density-plan.js
@@ -0,0 +1,225 @@
+import { clone, filter, map as mapToArray } from 'lodash'
+
+import Plan from './plan'
+import { debug } from './utils'
+
+// ===================================================================
+
+export default class DensityPlan extends Plan {
+  _checkRessourcesThresholds (objects, averages) {
+    return filter(objects, object =>
+      averages[object.id].memoryFree > this._thresholds.memoryFree.low
+    )
+  }
+
+  async execute () {
+    const results = await this._findHostsToOptimize()
+
+    if (!results) {
+      return
+    }
+
+    const {
+      hosts,
+      toOptimize
+    } = results
+
+    let {
+      averages: hostsAverages
+    } = results
+
+    const pools = await this._getPlanPools()
+    let optimizationsCount = 0
+
+    for (const hostToOptimize of toOptimize) {
+      const {
+        id: hostId,
+        $poolId: poolId
+      } = hostToOptimize
+
+      const {
+        master: masterId
+      } = pools[poolId]
+
+      // Avoid master optimization.
+      if (masterId === hostId) {
+        continue
+      }
+
+      // A host to optimize needs the ability to be restarted.
+      if (hostToOptimize.powerOnMode === '') {
+        debug(`Host (${hostId}) does not have a power on mode.`)
+        continue
+      }
+
+      let poolMaster // Pool master.
+      const poolHosts = [] // Without master.
+      const masters = [] // Without the master of this loop.
+      const otherHosts = []
+
+      for (const dest of hosts) {
+        const {
+          id: destId,
+          $poolId: destPoolId
+        } = dest
+
+        // Destination host != Host to optimize!
+        if (destId === hostId) {
+          continue
+        }
+
+        if (destPoolId === poolId) {
+          if (destId === masterId) {
+            poolMaster = dest
+          } else {
+            poolHosts.push(dest)
+          }
+        } else if (destId === pools[destPoolId].master) {
+          masters.push(dest)
+        } else {
+          otherHosts.push(dest)
+        }
+      }
+
+      const simulResults = await this._simulate({
+        host: hostToOptimize,
+        destinations: [
+          [ poolMaster ],
+          poolHosts,
+          masters,
+          otherHosts
+        ],
+        hostsAverages: clone(hostsAverages)
+      })
+
+      if (simulResults) {
+        // Update stats.
+        hostsAverages = simulResults.hostsAverages
+
+        // Migrate.
+        await this._migrate(hostId, simulResults.moves)
+        optimizationsCount++
+      }
+    }
+
+    debug(`Density mode: ${optimizationsCount} optimizations.`)
+  }
+
+  async _simulate ({ host, destinations, hostsAverages }) {
+    const { id: hostId } = host
+
+    debug(`Try to optimize Host (${hostId}).`)
+
+    const vms = await this._getVms(hostId)
+    const vmsAverages = await this._getVmsAverages(vms, host)
+
+    for (const vm of vms) {
+      if (!vm.xenTools) {
+        debug(`VM (${vm.id}) of Host (${hostId}) does not support pool migration.`)
+        return
+      }
+    }
+
+    // Sort vms by amount of memory. (+ -> -)
+    vms.sort((a, b) =>
+      vmsAverages[b.id].memory - vmsAverages[a.id].memory
+    )
+
+    const simulResults = {
+      hostsAverages,
+      moves: []
+    }
+
+    // Try to find a destination for each VM.
+    for (const vm of vms) {
+      let move
+
+      // Simulate the VM move on a destinations set.
+      for (const subDestinations of destinations) {
+        move = this._testMigration({
+          vm,
+          destinations: subDestinations,
+          hostsAverages,
+          vmsAverages
+        })
+
+        // Destination found.
+        if (move) {
+          simulResults.moves.push(move)
+          break
+        }
+      }
+
+      // Unable to move a VM.
+      if (!move) {
+        return
+      }
+    }
+
+    // Done.
+    return simulResults
+  }
+
+  // Test if a VM migration on a destination (of a destinations set) is possible.
+  _testMigration ({ vm, destinations, hostsAverages, vmsAverages }) {
+    const {
+      _thresholds: {
+        critical: criticalThreshold
+      }
+    } = this
+
+    // Sort the destinations by available memory. (- -> +)
+    destinations.sort((a, b) =>
+      hostsAverages[a.id].memoryFree - hostsAverages[b.id].memoryFree
+    )
+
+    for (const destination of destinations) {
+      const destinationAverages = hostsAverages[destination.id]
+      const vmAverages = vmsAverages[vm.id]
+
+      // Unable to move the VM.
+      if (
+        destinationAverages.cpu + vmAverages.cpu >= criticalThreshold ||
+        destinationAverages.memoryFree - vmAverages.memory <= criticalThreshold
+      ) {
+        continue
+      }
+
+      // Move ok. Update stats.
+      destinationAverages.cpu += vmAverages.cpu
+      destinationAverages.memoryFree -= vmAverages.memory
+
+      // Available movement.
+      return {
+        vm,
+        destination
+      }
+    }
+  }
+
+  // Migrate the VMs of one host.
+  // Try to shutdown the VMs host.
+  async _migrate (hostId, moves) {
+    const xapiSrc = this.xo.getXapi(hostId)
+
+    await Promise.all(
+      mapToArray(moves, move => {
+        const {
+          vm,
+          destination
+        } = move
+        const xapiDest = this.xo.getXapi(destination)
+        debug(`Migrate VM (${vm.id}) to Host (${destination.id}) from Host (${vm.$container}).`)
+        return xapiDest.migrateVm(vm._xapiId, this.xo.getXapi(destination), destination._xapiId)
+      })
+    )
+
+    debug(`Shutdown Host (${hostId}).`)
+
+    try {
+      await xapiSrc.shutdownHost(hostId)
+    } catch (error) {
+      debug(`Unable to shutdown Host (${hostId}).`, error)
+    }
+  }
+}
diff --git a/packages/xo-server-load-balancer/src/index.js b/packages/xo-server-load-balancer/src/index.js
new file mode 100644
index 000000000..d6218d738
--- /dev/null
+++ b/packages/xo-server-load-balancer/src/index.js
@@ -0,0 +1,203 @@
+import EventEmitter from 'events'
+import eventToPromise from 'event-to-promise'
+import { CronJob } from 'cron'
+import { intersection, map as mapToArray, uniq } from 'lodash'
+
+import DensityPlan from './density-plan'
+import PerformancePlan from './performance-plan'
+import {
+  DEFAULT_CRITICAL_THRESHOLD_CPU,
+  DEFAULT_CRITICAL_THRESHOLD_MEMORY_FREE
+} from './plan'
+import {
+  EXECUTION_DELAY,
+  debug
+} from './utils'
+
+class Emitter extends EventEmitter {}
+
+// ===================================================================
+
+const PERFORMANCE_MODE = 0
+const DENSITY_MODE = 1
+
+// ===================================================================
+
+export const configurationSchema = {
+  type: 'object',
+
+  properties: {
+    plans: {
+      type: 'array',
+      description: 'an array of plans',
+      title: 'Plans',
+
+      items: {
+        type: 'object',
+        title: 'Plan',
+
+        properties: {
+          name: {
+            type: 'string',
+            title: 'Name'
+          },
+
+          mode: {
+            enum: [ 'Performance mode', 'Density mode' ],
+            title: 'Mode'
+          },
+
+          pools: {
+            type: 'array',
+            description: 'list of pools where to apply the policy',
+
+            items: {
+              type: 'string',
+              $type: 'Pool'
+            }
+          },
+
+          thresholds: {
+            type: 'object',
+            title: 'Critical thresholds',
+
+            properties: {
+              cpu: {
+                type: 'integer',
+                title: 'CPU (%)',
+                default: DEFAULT_CRITICAL_THRESHOLD_CPU
+              },
+              memoryFree: {
+                type: 'integer',
+                title: 'RAM, Free memory (MB)',
+                default: DEFAULT_CRITICAL_THRESHOLD_MEMORY_FREE
+              }
+            }
+          },
+
+          excludedHosts: {
+            type: 'array',
+            title: 'Excluded hosts',
+            description: 'list of hosts that are not affected by the plan',
+
+            items: {
+              type: 'string',
+              $type: 'Host'
+            }
+          }
+        },
+
+        required: [ 'name', 'mode', 'pools' ]
+      },
+
+      minItems: 1
+    }
+  },
+
+  additionalProperties: false
+}
+
+// ===================================================================
+
+// Create a job not enabled by default.
+// A job is a cron task, a running and enabled state.
+const makeJob = (cronPattern, fn) => {
+  const job = {
+    running: false,
+    emitter: new Emitter()
+  }
+
+  job.cron = new CronJob(cronPattern, async () => {
+    if (job.running) {
+      return
+    }
+
+    job.running = true
+
+    try {
+      await fn()
+    } catch (error) {
+      console.error('[WARN] scheduled function:', error && error.stack || error)
+    } finally {
+      job.running = false
+      job.emitter.emit('finish')
+    }
+  })
+
+  job.isEnabled = () => job.cron.running
+
+  return job
+}
+
+// ===================================================================
+// ===================================================================
+
+class LoadBalancerPlugin {
+  constructor (xo) {
+    this.xo = xo
+    this._job = makeJob(`*/${EXECUTION_DELAY} * * * *`, ::this._executePlans)
+    this._emitter
+  }
+
+  async configure ({ plans }) {
+    const job = this._job
+    const enabled = job.isEnabled()
+
+    if (enabled) {
+      job.cron.stop()
+    }
+
+    // Wait until all old plans stopped running.
+    if (job.running) {
+      await eventToPromise(job.emitter, 'finish')
+    }
+
+    this._plans = []
+    this._poolIds = [] // Used pools.
+
+    if (plans) {
+      for (const plan of plans) {
+        this._addPlan(plan.mode === 'Performance mode' ? PERFORMANCE_MODE : DENSITY_MODE, plan)
+      }
+    }
+
+    if (enabled) {
+      job.cron.start()
+    }
+  }
+
+  load () {
+    this._job.cron.start()
+  }
+
+  unload () {
+    this._job.cron.stop()
+  }
+
+  _addPlan (mode, { name, pools, ...options }) {
+    pools = uniq(pools)
+
+    // Check already used pools.
+    if (intersection(pools, this._poolIds).length > 0) {
+      throw new Error(`Pool(s) already included in an other plan: ${pools}`)
+    }
+
+    this._poolIds = this._poolIds.concat(pools)
+    this._plans.push(mode === PERFORMANCE_MODE
+      ? new PerformancePlan(this.xo, name, pools, options)
+      : new DensityPlan(this.xo, name, pools, options)
+    )
+  }
+
+  _executePlans () {
+    debug('Execute plans!')
+
+    return Promise.all(
+      mapToArray(this._plans, plan => plan.execute())
+    )
+  }
+}
+
+// ===================================================================
+
+export default ({ xo }) => new LoadBalancerPlugin(xo)
diff --git a/packages/xo-server-load-balancer/src/performance-plan.js b/packages/xo-server-load-balancer/src/performance-plan.js
new file mode 100644
index 000000000..fc0b3e6c2
--- /dev/null
+++ b/packages/xo-server-load-balancer/src/performance-plan.js
@@ -0,0 +1,138 @@
+import { filter, find, map as mapToArray } from 'lodash'
+
+import Plan from './plan'
+import { debug } from './utils'
+
+// Compare a list of objects and give the best.
+function searchBestObject (objects, fun) {
+  let object = objects[0]
+
+  for (let i = 1; i < objects.length; i++) {
+    if (fun(object, objects[i]) > 0) {
+      object = objects[i]
+    }
+  }
+
+  return object
+}
+
+// ===================================================================
+
+export default class PerformancePlan extends Plan {
+  _checkRessourcesThresholds (objects, averages) {
+    return filter(objects, object => {
+      const objectAverages = averages[object.id]
+
+      return (
+        objectAverages.cpu >= this._thresholds.cpu.high ||
+        objectAverages.memoryFree <= this._thresholds.memoryFree.high
+      )
+    })
+  }
+
+  async execute () {
+    // Try to power on a hosts set.
+    try {
+      await Promise.all(
+        mapToArray(
+          filter(this._getHosts({ powerState: 'Halted' }), host => host.powerOnMode !== ''),
+          host => {
+            const { id } = host
+            return this.xo.getXapi(id).powerOnHost(id)
+          }
+        )
+      )
+    } catch (error) {
+      console.error(error)
+    }
+
+    const results = await this._findHostsToOptimize()
+
+    if (!results) {
+      return
+    }
+
+    const {
+      averages,
+      toOptimize
+    } = results
+    let { hosts } = results
+
+    toOptimize.sort((a, b) => {
+      a = averages[a.id]
+      b = averages[b.id]
+
+      return (b.cpu - a.cpu) || (a.memoryFree - b.memoryFree)
+    })
+
+    for (const exceededHost of toOptimize) {
+      const { id } = exceededHost
+
+      debug(`Try to optimize Host (${exceededHost.id}).`)
+      hosts = filter(hosts, host => host.id !== id)
+
+      // Search bests combinations for the worst host.
+      await this._optimize({
+        exceededHost,
+        hosts,
+        hostsAverages: averages
+      })
+    }
+  }
+
+  async _optimize ({ exceededHost, hosts, hostsAverages }) {
+    const vms = await this._getVms(exceededHost.id)
+    const vmsAverages = await this._getVmsAverages(vms, exceededHost)
+
+    // Sort vms by cpu usage. (lower to higher)
+    vms.sort((a, b) =>
+      vmsAverages[b.id].cpu - vmsAverages[a.id].cpu
+    )
+
+    const exceededAverages = hostsAverages[exceededHost.id]
+    const promises = []
+
+    const xapiSrc = this.xo.getXapi(exceededHost)
+    let optimizationsCount = 0
+
+    const searchFunction = (a, b) => hostsAverages[b.id].cpu - hostsAverages[a.id].cpu
+
+    for (const vm of vms) {
+      // Search host with lower cpu usage in the same pool first. In other pool if necessary.
+      let destination = searchBestObject(find(hosts, host => host.$poolId === vm.$poolId), searchFunction)
+
+      if (!destination) {
+        destination = searchBestObject(hosts, searchFunction)
+      }
+
+      const destinationAverages = hostsAverages[destination.id]
+      const vmAverages = vmsAverages[vm.id]
+
+      // Unable to move the vm.
+      if (
+        exceededAverages.cpu - vmAverages.cpu < destinationAverages.cpu + vmAverages.cpu ||
+        destinationAverages.memoryFree > vmAverages.memory
+      ) {
+        continue
+      }
+
+      exceededAverages.cpu -= vmAverages.cpu
+      destinationAverages.cpu += vmAverages.cpu
+
+      exceededAverages.memoryFree += vmAverages.memory
+      destinationAverages.memoryFree -= vmAverages.memory
+
+      debug(`Migrate VM (${vm.id}) to Host (${destination.id}) from Host (${exceededHost.id}).`)
+      optimizationsCount++
+
+      promises.push(
+        xapiSrc.migrateVm(vm._xapiId, this.xo.getXapi(destination), destination._xapiId)
+      )
+    }
+
+    await Promise.all(promises)
+    debug(`Performance mode: ${optimizationsCount} optimizations for Host (${exceededHost.id}).`)
+
+    return
+  }
+}
diff --git a/packages/xo-server-load-balancer/src/plan.js b/packages/xo-server-load-balancer/src/plan.js
new file mode 100644
index 000000000..4ac09c057
--- /dev/null
+++ b/packages/xo-server-load-balancer/src/plan.js
@@ -0,0 +1,253 @@
+import { filter, includes, map as mapToArray } from 'lodash'
+
+import {
+  EXECUTION_DELAY,
+  debug
+} from './utils'
+
+const MINUTES_OF_HISTORICAL_DATA = 30
+
+// CPU threshold in percent.
+export const DEFAULT_CRITICAL_THRESHOLD_CPU = 90.0
+
+// Memory threshold in MB.
+export const DEFAULT_CRITICAL_THRESHOLD_MEMORY_FREE = 64.0
+
+// Thresholds factors.
+const HIGH_THRESHOLD_FACTOR = 0.85
+const LOW_THRESHOLD_FACTOR = 0.25
+
+const HIGH_THRESHOLD_MEMORY_FREE_FACTOR = 1.25
+const LOW_THRESHOLD_MEMORY_FREE_FACTOR = 20.0
+
+const numberOrDefault = (value, def) => (value >= 0) ? value : def
+
+// ===================================================================
+// Averages.
+// ===================================================================
+
+function computeAverage (values, nPoints = values.length) {
+  let sum = 0
+  let tot = 0
+
+  const { length } = values
+
+  for (let i = length - nPoints; i < length; i++) {
+    const value = values[i]
+
+    sum += value || 0
+
+    if (value) {
+      tot += 1
+    }
+  }
+
+  return sum / tot
+}
+
+function computeRessourcesAverage (objects, objectsStats, nPoints) {
+  const averages = {}
+
+  for (const object of objects) {
+    const { id } = object
+    const { stats } = objectsStats[id]
+
+    averages[id] = {
+      cpu: computeAverage(
+        mapToArray(stats.cpus, cpu => computeAverage(cpu, nPoints))
+      ),
+      nCpus: stats.cpus.length,
+      memoryFree: computeAverage(stats.memoryFree, nPoints),
+      memory: computeAverage(stats.memory, nPoints)
+    }
+  }
+
+  return averages
+}
+
+function computeRessourcesAverageWithWeight (averages1, averages2, ratio) {
+  const averages = {}
+
+  for (const id in averages1) {
+    const objectAverages = averages[id] = {}
+
+    for (const averageName in averages1[id]) {
+      objectAverages[averageName] = averages1[id][averageName] * ratio + averages2[id][averageName] * (1 - ratio)
+    }
+  }
+
+  return averages
+}
+
+function setRealCpuAverageOfVms (vms, vmsAverages, nCpus) {
+  for (const vm of vms) {
+    const averages = vmsAverages[vm.id]
+    averages.cpu *= averages.nCpus / nCpus
+  }
+}
+
+// ===================================================================
+
+export default class Plan {
+  constructor (xo, name, poolIds, {
+    excludedHosts,
+    thresholds
+  } = {}) {
+    this.xo = xo
+    this._name = name
+    this._poolIds = poolIds
+    this._excludedHosts = excludedHosts
+    this._thresholds = {
+      cpu: {
+        critical: numberOrDefault(thresholds && thresholds.cpu, DEFAULT_CRITICAL_THRESHOLD_CPU)
+      },
+      memoryFree: {
+        critical: numberOrDefault(thresholds && thresholds.memoryFree, DEFAULT_CRITICAL_THRESHOLD_MEMORY_FREE) * 1024
+      }
+    }
+
+    for (const key in this._thresholds) {
+      const attr = this._thresholds[key]
+      const { critical } = attr
+
+      if (key === 'memoryFree') {
+        attr.high = critical * HIGH_THRESHOLD_MEMORY_FREE_FACTOR
+        attr.low = critical * LOW_THRESHOLD_MEMORY_FREE_FACTOR
+      } else {
+        attr.high = critical * HIGH_THRESHOLD_FACTOR
+        attr.low = critical * LOW_THRESHOLD_FACTOR
+      }
+    }
+  }
+
+  execute () {
+    throw new Error('Not implemented')
+  }
+
+  // ===================================================================
+  // Get hosts to optimize.
+  // ===================================================================
+
+  async _findHostsToOptimize () {
+    const hosts = this._getHosts()
+    const hostsStats = await this._getHostsStats(hosts, 'minutes')
+
+    // Check if a ressource's utilization exceeds threshold.
+    const avgNow = computeRessourcesAverage(hosts, hostsStats, EXECUTION_DELAY)
+    let toOptimize = this._checkRessourcesThresholds(hosts, avgNow)
+
+    // No ressource's utilization problem.
+    if (toOptimize.length === 0) {
+      debug('No hosts to optimize.')
+      return
+    }
+
+    // Check in the last 30 min interval with ratio.
+    const avgBefore = computeRessourcesAverage(hosts, hostsStats, MINUTES_OF_HISTORICAL_DATA)
+    const avgWithRatio = computeRessourcesAverageWithWeight(avgNow, avgBefore, 0.75)
+
+    toOptimize = this._checkRessourcesThresholds(toOptimize, avgWithRatio)
+
+    // No ressource's utilization problem.
+    if (toOptimize.length === 0) {
+      debug('No hosts to optimize.')
+      return
+    }
+
+    return {
+      toOptimize,
+      averages: avgWithRatio,
+      hosts
+    }
+  }
+
+  _checkRessourcesThresholds () {
+    throw new Error('Not implemented')
+  }
+
+  // ===================================================================
+  // Get objects.
+  // ===================================================================
+
+  _getPlanPools () {
+    const pools = {}
+
+    try {
+      for (const poolId of this._poolIds) {
+        pools[poolId] = this.xo.getObject(poolId)
+      }
+    } catch (_) {
+      return {}
+    }
+
+    return pools
+  }
+
+  // Compute hosts for each pool. They can change over time.
+  _getHosts ({ powerState = 'Running' } = {}) {
+    return filter(this.xo.getObjects(), object => (
+      object.type === 'host' &&
+      includes(this._poolIds, object.$poolId) &&
+      object.power_state === powerState &&
+      !includes(this._excludedHosts, object.id)
+    ))
+  }
+
+  async _getVms (hostId) {
+    return filter(this.xo.getObjects(), object =>
+      object.type === 'VM' &&
+      object.power_state === 'Running' &&
+      object.$container === hostId
+    )
+  }
+
+  // ===================================================================
+  // Get stats.
+  // ===================================================================
+
+  async _getHostsStats (hosts, granularity) {
+    const hostsStats = {}
+
+    await Promise.all(mapToArray(hosts, host =>
+      this.xo.getXapiHostStats(host, granularity).then(hostStats => {
+        hostsStats[host.id] = {
+          nPoints: hostStats.stats.cpus[0].length,
+          stats: hostStats.stats,
+          averages: {}
+        }
+      })
+    ))
+
+    return hostsStats
+  }
+
+  async _getVmsStats (vms, granularity) {
+    const vmsStats = {}
+
+    await Promise.all(mapToArray(vms, vm =>
+      this.xo.getXapiVmStats(vm, granularity).then(vmStats => {
+        vmsStats[vm.id] = {
+          nPoints: vmStats.stats.cpus[0].length,
+          stats: vmStats.stats,
+          averages: {}
+        }
+      })
+    ))
+
+    return vmsStats
+  }
+
+  async _getVmsAverages (vms, host) {
+    const vmsStats = await this._getVmsStats(vms, 'minutes')
+    const vmsAverages = computeRessourcesAverageWithWeight(
+      computeRessourcesAverage(vms, vmsStats, EXECUTION_DELAY),
+      computeRessourcesAverage(vms, vmsStats, MINUTES_OF_HISTORICAL_DATA),
+      0.75
+    )
+
+    // Compute real CPU usage. Virtuals cpus to reals cpus.
+    setRealCpuAverageOfVms(vms, vmsAverages, host.CPUs.cpu_count)
+
+    return vmsAverages
+  }
+}
diff --git a/packages/xo-server-load-balancer/src/utils.js b/packages/xo-server-load-balancer/src/utils.js
new file mode 100644
index 000000000..f7894a639
--- /dev/null
+++ b/packages/xo-server-load-balancer/src/utils.js
@@ -0,0 +1,13 @@
+const noop = () => {}
+
+const LOAD_BALANCER_DEBUG = 1
+
+// Delay between each ressources evaluation in minutes.
+// Must be less than MINUTES_OF_HISTORICAL_DATA.
+export const EXECUTION_DELAY = 1
+
+// ===================================================================
+
+export const debug = LOAD_BALANCER_DEBUG
+  ? str => console.log(`[load-balancer]${str}`)
+  : noop