def crossover(self):
"""Crossover operation.
- Select two random chromosomes
- Rank their genes according to an efficiency function
- Create a new chromosome by taking the "best" genes until all VNFs are placed
(if when adding a gene one of its VNFs is already placed, just ignore it)
"""
# Pick two random chromosomes (C1 and C2 could coincide)
C1 = choice(self.solution_pool)
C2 = choice(self.solution_pool)
# Create a list of all their genes (i.e., hosts with the VNFs assigned to them)
genes = copy.deepcopy(C1.genes + C2.genes)
# sort genes by efficiency (lowest cost first)
for g in genes:
g.efficiency = self.gene_efficiency(g)
# For availability, sort in descending order (as we want the max here)
rev = False
if self.optimize_for == "availability":
rev = True
genes = sorted(genes, key=attrgetter('efficiency'), reverse=rev)
# vnfs to place (list of strings)
vnfs = [v["vnf_name"] for v in self.scenario["vnfs"]]
# create new chromosome
new_genes = []
# continue as long as there are still vnfs to place
while vnfs and genes:
# if the gene host has already been put in the chromosome,
# skip the gene. This ensures that at this step no capacity
# constraints will be violated.
if genes[0].hostname in [g.hostname for g in new_genes]:
del (genes[0])
else:
# if a VNF of the gene is not in the remaining vnf list, remove it from the gene
# since this means it's already placed
for v in genes[0].vnfs:
if v["vnf_name"] not in vnfs:
genes[0].vnfs.remove(v)
# finally, add the new gene
# also, remove its vnfs from the list of pending ones (there should be a more efficient way to do this)
new_genes.append(
Gene(genes[0].hostname,
genes[0].vnfs,
host_failure_rate=genes[0].host_failure_rate))
for v in genes[0].vnfs:
if v["vnf_name"] in vnfs:
vnfs.remove(v["vnf_name"])
del (genes[0])
C = Chromosome(new_genes)
# Now we need to check if there are any VNFs left unassigned
# If so, we place them anywhere they fit and are allowed to
solution = copy.deepcopy(self.scenario)
helpers.from_chromosome(solution, C)
while vnfs:
vname = vnfs.pop()
v = filter(lambda x: x.get("vnf_name") == vname,
solution["vnfs"])[0]
host = helpers.check_if_there_is_space(solution, v)
if host: # host found, place VNF
v["place_at"].append(host["host_name"])
else:
# Normally we should not arrive here, but, if so,
# this means that there's nowhere to place the VNF
# in this case, we return None and the caller will see what to do
return None
# perform constraint checks
mec_constraints_ok = helpers.check_mec_constraints(solution)
location_constraints_ok = helpers.check_location_constraints(solution)
link_constraints_ok = helpers.check_link_capacity_constraints(solution)
delay_constraints_ok = helpers.check_delay_constraints(solution)
if link_constraints_ok and delay_constraints_ok and mec_constraints_ok and location_constraints_ok:
# return the chromosome
return helpers.to_chromosome(solution)
else:
return None
def mutation(self):
"""Mutation operator.
For each chromosome in the solution pool, decide according to the mutation
rate if we'll modify it or not. If its selected for mutation, we create a
mutant as follows: We select two random hosts and swap two random VNFs. If
none of the selected hosts has VNFs on it, we select two other hosts and so on.
If the constraints are violated, the mutant is rejected.
"""
counter = 0
for s in self.solution_pool:
if uniform(0, 1) <= self.mutation_rate:
logging.debug("Mutating solution: " + str(s))
# create a copy of the chromosome
scopy = copy.deepcopy(s)
# Corner-case: There's just one gene in the chromosomes, so nothing to
# mutate
if len(scopy.genes) < 2:
continue
# pick two hosts
while True:
h1 = choice(scopy.genes)
h2 = choice(scopy.genes)
if h1 == h2:
continue
if h1.vnfs or h2.vnfs:
break
# pick one VNF from each host
v1 = None
v2 = None
if h1.vnfs:
v1 = choice(h1.vnfs)
h1.vnfs = [
x for x in h1.vnfs if x["vnf_name"] != v1["vnf_name"]
]
if h2.vnfs:
v2 = choice(h2.vnfs)
h2.vnfs = [
x for x in h2.vnfs if x["vnf_name"] != v2["vnf_name"]
]
# swap the two VNFs
if v2:
h1.vnfs.append(v2)
if v1:
h2.vnfs.append(v1)
# create a solution represented in the full format
S = helpers.from_chromosome(self.scenario, scopy)
reject = False
# check constraints
for v in S["vnfs"]:
hname = v["place_at"][0]
vname = v["vnf_name"]
if not helpers.check_if_placement_allowed(S, hname, vname):
# There's a VNF "illegally" placed
reject = True
break
if not reject:
if helpers.check_mec_constraints(S) is False:
reject = True
if not reject:
if helpers.check_location_constraints(S) is False:
reject = True
if not reject:
for h in S["hosts"]:
if helpers.check_host_capacity_constraint(S,
h) is False:
reject = True
break
if not reject:
if helpers.check_link_capacity_constraints(S) is False:
reject = True
if not reject:
if helpers.check_delay_constraints(S) is False:
reject = True
mutant = helpers.to_chromosome(S)
if not reject:
# all constraints ok
# delete old solution and replace with mutant
self.solution_pool[counter] = mutant
logging.debug("Mutant ACCEPTED")
else:
logging.debug("Mutant REJECTED")
pass
counter += 1
def init_solution_pool(self):
"""Initialize solution pool.
Generate S feasible solutions/placements as follows: For each VNF,
select a random host. If it has enough capacity, place VNF there.
Otherwise look for another host.
"""
self.solution_pool = []
solutions_to_generate = self.solution_pool_size
while solutions_to_generate > 0:
# TODO: Remove the deepcopy, just clear "place_at" fields
solution = copy.deepcopy(self.scenario)
reset = False
for v in solution['vnfs']:
if reset is True:
# Solution infeasible. Try another one...
logging.debug("Infeasible solution. Resetting")
break
vnf_placed = False
while not vnf_placed:
if not helpers.check_if_there_is_space(solution, v):
# reset solution and start from scratch
reset = True
break
h = choice(solution["hosts"])
v["place_at"] = [h["host_name"]]
# First check if it is allowed to place v at h
# If not, try another one
if not helpers.check_if_placement_allowed(
solution, h["host_name"], v["vnf_name"]):
logging.debug(
"init_solution_pool: Not allowed, trying another host"
)
v["place_at"] = None
continue
# check if h has the available resources to host v
# If capacity will be exceeded, try another host
if helpers.check_host_capacity_constraint(solution, h):
vnf_placed = True
logging.debug("init_solution_pool: VNF " +
v["vnf_name"] + " placed at " +
h["host_name"])
else:
v["place_at"] = None
# check if the solution violates any MEC constraints
mec_constraints_ok = helpers.check_mec_constraints(solution)
if not mec_constraints_ok:
logging.debug("init_solution_pool: Mec constraint violated")
continue
# check if we're violating location constraints
location_constraints_ok = helpers.check_location_constraints(
solution)
if not location_constraints_ok:
logging.debug(
"init_solution_pool: Location constraint violated")
continue
# Check if the solution violates any link capacities
link_constraints_ok = helpers.check_link_capacity_constraints(
solution)
if not link_constraints_ok:
logging.debug(
"init_solution_pool: Link capacity constraint violated")
continue
delay_constraints_ok = helpers.check_delay_constraints(solution)
if not delay_constraints_ok:
logging.debug("init_solution_pool: Delay constraint violated")
continue
#reachability_ok = helpers.check_reachability(solution)
#if not reachability_ok:
# continue
if reset is False:
logging.debug(helpers.show_host_link_status(solution))
logging.debug(
"Solution cost: " +
str(helpers.get_solution_cost(solution)) +
", availability: " +
str(helpers.get_solution_availability(solution)) +
", latency: " +
str(helpers.get_solution_global_latency(solution)))
# Store the simplified "chromosome" representation of the solution
C = helpers.to_chromosome(solution)
self.solution_pool.append(C)
solutions_to_generate -= 1