def select_host(hosts,
ranking_string=None,
blacklist=None,
blacklist_name=None):
"""Select a host from the provided list.
If no ranking is provided (in `ranking_string`) then random selection
is used.
Args:
hosts (list):
List of host names to choose from.
NOTE: Host names must be identifiable from the host where the
call is executed.
ranking_string (str):
A multiline string containing Python expressions to filter
hosts by e.g::
# only consider hosts with less than 70% cpu usage
# and a server load of less than 5
cpu_percent() < 70
getloadavg()[0] < 5
And or Python statements to rank hosts by e.g::
# rank by used cpu, then by load average as a tie-break
# (lower scores are better)
cpu_percent()
getloadavg()
Comments are allowed using `#` but not inline comments.
blacklist (list):
List of host names to filter out.
Can be short host names (do not have to be fqdn values)
blacklist_name (str):
The reason for blacklisting these hosts
(used for exceptions).
Raises:
HostSelectException:
In the event that no hosts are available / meet the specified
criterion.
socket.gaierror:
This may be raised in the event of unknown host names
for some installations or not for others.
Returns:
tuple - (hostname, fqdn) the chosen host
hostname (str):
The hostname as provided to this function.
fqdn (str):
The fully qualified domain name of this host.
"""
# standardise host names - remove duplicate items
hostname_map = { # note dictionary keys filter out duplicates
get_fqdn_by_host(host): host
for host in hosts
}
hosts = list(hostname_map)
if blacklist:
blacklist = list(set(map(get_fqdn_by_host, blacklist)))
# dict of conditions and whether they have been met (for error reporting)
data = {host: {} for host in hosts}
# filter out `filter_hosts` if provided
if blacklist:
hosts, data = _filter_by_hostname(hosts,
blacklist,
blacklist_name,
data=data)
if not hosts:
# no hosts provided / left after filtering
raise HostSelectException(data)
rankings = []
if ranking_string:
# parse rankings
rankings = list(_get_rankings(ranking_string))
if not rankings:
# no metrics or ranking required, pick host at random
hosts = [random.choice(list(hosts))] # nosec
if not rankings and len(hosts) == 1:
return hostname_map[hosts[0]], hosts[0]
# filter and sort by rankings
metrics = list({x for x, _ in rankings}) # required metrics
results, data = _get_metrics( # get data from each host
hosts, metrics, data)
hosts = list(results) # some hosts might not be contactable
# stop here if we don't need to proceed
if not hosts:
# no hosts provided / left after filtering
raise HostSelectException(data)
if not rankings and len(hosts) == 1:
return hostname_map[hosts[0]], hosts[0]
hosts, data = _filter_by_ranking(
# filter by rankings, sort by ranking
hosts,
rankings,
results,
data=data)
if not hosts:
# no hosts provided / left after filtering
raise HostSelectException(data)
return hostname_map[hosts[0]], hosts[0]
def select_suite_host(**_):
raise HostSelectException({})
def select_workflow_host(**_):
raise HostSelectException({})