Request mechanism rolled out, migration mechanism is also incorporated

helper.py

@@ -0,0 +1,117 @@
+from collections import Counter
+from functools import reduce
+
+from ucloud_common.vm import VmPool, VMStatus
+from ucloud_common.host import HostPool, HostStatus
+from ucloud_common.request import RequestEntry, RequestPool, RequestType
+
+from etcd3_wrapper import Etcd3Wrapper
+from decouple import config
+
+client = Etcd3Wrapper(
+        host=config("ETCD_HOST"), port=int(config("ETCD_PORT"))
+    )
+vm_pool = VmPool(client, config("VM_PREFIX"))
+host_pool = HostPool(client, config("HOST_PREFIX"))
+request_pool = RequestPool(client, config("REQUEST_PREFIX"))
+
+
+def accumulated_specs(vms_specs):
+    if not vms_specs:
+        return {}
+    return reduce((lambda x, y: Counter(x) + Counter(y)), vms_specs)
+
+
+def remaining_resources(host_specs, vms_specs):
+    """Return remaining resources host_specs - vms"""
+    vms_specs = Counter(vms_specs)
+    remaining = Counter(host_specs)
+    remaining.subtract(vms_specs)
+
+    return remaining
+
+
+def get_suitable_host(vm_specs, hosts=None):
+    if hosts is None:
+        hosts = host_pool.by_status(HostStatus.alive)
+
+    for host in hosts:
+        # Filter them by host_name
+        vms = vm_pool.by_host(host.key)
+
+        # Filter them by status
+        vms = vm_pool.except_status(VMStatus.requested_new, vms)
+
+        running_vms_specs = [vm.specs for vm in vms]
+        # Accumulate all of their combined specs
+        running_vms_accumulated_specs = accumulated_specs(
+            running_vms_specs
+        )
+
+        # Find out remaining resources after
+        # host_specs - already running vm_specs
+        remaining = remaining_resources(
+            host.specs, running_vms_accumulated_specs
+        )
+
+        # Find out remaining - new_vm_specs
+        remaining = remaining_resources(remaining, vm_specs)
+        # if remaining resources >= 0 return this host_name
+        if all(
+                map(
+                    lambda x: True if remaining[x] >= 0 else False,
+                    remaining,
+                )
+        ):
+            return host.key
+
+    return None
+
+
+def dead_host_detection():
+    # Bring out your dead! - Monty Python and the Holy Grail
+    hosts = host_pool.by_status(HostStatus.alive)
+    dead_hosts_keys = []
+
+    for host in hosts:
+        # Only check those who claims to be alive
+        if host.status == HostStatus.alive:
+            if not host.is_alive():
+                dead_hosts_keys.append(host.key)
+
+    return dead_hosts_keys
+
+
+def dead_host_mitigation(dead_hosts_keys):
+    for host_key in dead_hosts_keys:
+        host = host_pool.get(host_key)
+        host.declare_dead()
+
+        vms_hosted_on_dead_host = vm_pool.by_host(host_key)
+        for vm in vms_hosted_on_dead_host:
+            vm.declare_killed()
+            vm_pool.put(vm)
+        host_pool.put(host)
+
+
+def assign_host(vm):
+    host_name = get_suitable_host(vm.specs)
+    if host_name:
+        # if vm.status == VMStatus.requested_new:
+        #     vm.status = VMStatus.scheduled_deploy
+        #
+        # if vm.status == VMStatus.killed:
+        #     vm.status = VMStatus.requested_start
+
+        vm.hostname = host_name
+        vm_pool.put(vm)
+
+        r = RequestEntry.from_scratch(type=RequestType.StartVM,
+                                      uuid=vm.uuid,
+                                      hostname=vm.hostname)
+        request_pool.put(r)
+
+        vm.log.append("VM scheduled for starting")
+
+        return host_name
+    return None