While I agree that this is not a very production-like configuration, I think it's good to recognize that there are plenty of clusters out there where more than five zookeeper nodes are called for. I run systems routinely with seven voting members plus three or more observers, for reasons having to do with system behavior during network split scenarios in AWS EC2. Mac OS specific issues aside, it would be unfortunate if there were an artificial cap on the number of nodes in a machine-local test cluster, especially if it were related to an ICMP storm scenario.
On Thu, Jan 23, 2020, 8:11 AM Ted Dunning <ted.dunn...@gmail.com> wrote: > I think that this is far outside the normal operation bounds and has an > easy work-around. > > First, it is very uncommon to run more than 5 ZK nodes. Running 23 on a > single host is bizarre (viewed from an operational lens). > > Second, there is a simple configuration change that makes the strange > configuration work anyway. > > A third point unrelated to operational considerations is that there is risk > in making a last minute changes to code. That risk is borne by normal > configurations as well as these unusual ones. > > In sum, > > - this might look like a P1 (system down) issue, but there is a workaround > so it is certainly no more than P2 > > - even P2 is unwarranted because the is a non-production configuration > > - a P3 issue isn't a stop-ship issue. > > > > On Fri, Jan 17, 2020 at 5:17 AM Szalay-Bekő Máté < > szalay.beko.m...@gmail.com> > wrote: > > > TLDR: > > During testing RC for 3.6.0, we found that ZooKeeper cluster with large > > number of ensemble members (e.g. 23) can not start properly. This issue > > seems to happen only on mac, and a workaround is to disable the ICMP > > throttling. The question is if this workaround is enough for the RC, or > if > > we should change the code in ZooKeeper to limit the number of ICMP > > requests. > > > > > > The problem: > > > > On linux, I haven't been able to reproduce the problem. I tried with 5, > 9, > > 15 and 23 ensemble members and the quorum always seems to start properly > in > > a few seconds. (I used OpenJDK 1.8.232 on Ubuntu 18.04) > > > > On mac, the problem is consistently happening for large ensembles. The > > server is very slow to start and we see a lot of warnings in the log like > > these: > > > > 2020-01-15 20:02:13,431 [myid:13] - WARN > > [ListenerHandler-phunt-MBP13.local/192.168.1.91:4193 > :QuorumCnxManager@691 > > ] > > - None of the addresses (/192.168.1.91:4190) are reachable for sid 10 > > java.net.NoRouteToHostException: No valid address among [/ > > 192.168.1.91:4190] > > > > 2020-01-17 11:02:26,177 [myid:4] - WARN > > [Thread-2531:QuorumCnxManager$SendWorker@1269] - destination address / > > 127.0.0.1 not reachable anymore, shutting down the SendWorker for sid 6 > > > > The exception is happening when the new MultiAddress feature tries to > > filter the unreachable hosts from the address list when trying to decide > > which election address to connect. This involves the calling of the > > InetAddress.isReachable method with a default timeout of 500ms, which > goes > > down to a native call in java and basically try to do a ping (an ICMP > echo > > request) to the host. Naturally, the localhost should be always > reachable. > > This call gets timeouted on mac if we have many ensemble members. I > tested > > with 9 members and the cluster started properly. With 11-13-15 members it > > took more and more time to get the cluster to start, and the > > "NoRouteToHostException" started to appear in the logs. After around 1 > > minute the 15 ensemble members cluster started, but obviously this is way > > too long. > > > > On mac, we we have the ICMP rate limit set to 250 by default. You can > turn > > this off using the following command: sudo sysctl -w > > net.inet.icmp.icmplim=0 > > (see https://krypted.com/mac-os-x/disable-icmp-rate-limiting-os-x/) > > > > Using the above command before starting the 23 ensemble members cluster > > locally seems to solve the problem for me. (can someone verify?) The > > question is if this workaround is enough or not. > > > > As far as I can tell, the current code will generate 2*A*(M-1) ICMP calls > > in each ZooKeeper server during startup, if 'X' is the number of ensemble > > members and 'A' is the number of election addresses provided for each > > member. This is not that high, if each ZooKeeper server is started on a > > different machine, but if we start a lot of ZooKeeper servers on a single > > machine, then it can quickly go beyond the predefined limit of 250 for > mac. > > > > OPTION 1: we keep the code as it is. we might change the documentation > for > > zkconf mentioning this mac specific issue and the way how to disable the > > ICMP rate limit. > > > > OPTION 2: we change the code not to filter the list of election addresses > > if the list has only a single element. This seems to be a logical way to > > decrease the ICMP requests. However, if we would run a large number of > > ZooKeeper servers on a single machine using multiple election addresses > for > > each server, we would get the same problem (most probably even quicker) > > > > OPTION 3: make the address filtering configurable and change zkconf to > > disable it by default. (but disabling will make the quorum potentially > > unable to recover during network failures, so it is not recommended > during > > production) > > > > OPTION 4: refactor the MultiAddress feature and remove the ICMP calls > from > > the ZooKeeper code. However, it is clearly helps for the quick recovery > > during network failures... at the moment I can't think any good solution > to > > avoid it. > > > > Kind regards, > > Mate > > >
