A python counterpart of the following commit:
0b29edb5cbdc ("dns-resolve: Do not treat never accessed responses as
expired.")
The same issue exists in the python code where we may never connect
to a remote server if our DNS TTL is lower than the backoff interval.
Fix it in the same way as we did in C implementation - allow using
the entry if it was never used after requesting for up to 5 minutes,
as this is not really caching, but a "transaction in progress" type
of situation.
More details in the commit message for the C version.
Signed-off-by: Ilya Maximets <[email protected]>
---
python/ovs/dns_resolve.py | 29 ++++++++++++++++++++++++-----
1 file changed, 24 insertions(+), 5 deletions(-)
diff --git a/python/ovs/dns_resolve.py b/python/ovs/dns_resolve.py
index 41546ad5c..d38e8a658 100644
--- a/python/ovs/dns_resolve.py
+++ b/python/ovs/dns_resolve.py
@@ -29,12 +29,15 @@ import ovs.vlog
vlog = ovs.vlog.Vlog("dns_resolve")
+RESOLVE_UNUSED_TIMEOUT = 300 # Seconds.
+
class ReqState(enum.Enum):
INVALID = 0
PENDING = 1
- GOOD = 2
- ERROR = 3
+ GOOD_UNUSED = 2
+ GOOD = 4
+ ERROR = 5
class DNSRequest:
@@ -48,11 +51,27 @@ class DNSRequest:
@property
def expired(self):
- return time.time() > self.time + self.ttl
+ ttl = self.ttl
+ # When we just sent a request, but didn't look at the response yet,
+ # it's not caching, but a "transaction in progress" situation, so we
+ # can use the response even with TTL of 0 and more than 1 second
+ # passed. Allow such values to be accessed for at least
+ # RESOLVE_UNUSED_TIMEOUT seconds without considering them stale.
+ # This is necessary in case of large backoff intervals on connections
+ # or if the process is doing some other work not looking at the
+ # response for longer than TTL. */
+ if self.state == ReqState.GOOD_UNUSED:
+ ttl = max(ttl, RESOLVE_UNUSED_TIMEOUT)
+ # Not a "transaction in progress" anymore, normal caching rules
+ # should apply from this point forward.
+ self.state = ReqState.GOOD
+
+ return time.time() > self.time + ttl
@property
def is_valid(self):
- return self.state == ReqState.GOOD and not self.expired
+ return (self.state in [ReqState.GOOD_UNUSED, ReqState.GOOD]
+ and not self.expired)
def __str__(self):
return (f"DNSRequest(name={self.name}, state={self.state}, "
@@ -184,7 +203,7 @@ class DNSResolver:
# _callback causes a segfault. So just grab and store what we need.
req.result = str(ip)
req.ttl = result.ttl
- req.state = ReqState.GOOD
+ req.state = ReqState.GOOD_UNUSED
req.time = time.time()
except (ValueError, StopIteration):
req.state = ReqState.ERROR
--
2.52.0
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