Hi Yaroslav, Having a config option to advertise something else is what I can support. Needless to say the actual behavior would remain as default.
G On Mon, Aug 18, 2025 at 3:28 PM Yaroslav Chernysh <yaroche...@gmail.com> wrote: > Hi Gabor, > > I got your point on using `getHostName()`. Thank you for such a detailed > explanation. > > What do you think about advertising rest.address instead? In case of > YARN (at least on my environment), this is already set by YARN to a NM > hostname, so rDNS would be avoided. > > Thanks, > > Yaroslav > > > On 2025/08/15 21:12:58 Gabor Somogyi wrote: > > Hi Yaroslav, > > > > Thanks for your efforts in finding out all the details. > > > > I think making `getHostName` possible with a config + some additional > > warnings in the documentation can be considered. > > You need to evaluate your security standards but you win something on > one > > side and introduce new attack vector on the other side. > > > > I would write something similar in the documentation, and I also suggest > > you consider these for your own situation as well: > > - rDNS is not trustworthy for security decisions. Attackers with control > > over PTR (or via poisoning/misconfig) can return arbitrary names. > > MITRE tracks this as CWE-350 [1] (Reliance on Reverse DNS for > Security). If > > you base TLS host checks on rDNS, it’s bypassable. > > - Slow or failing DNS causes blocking delays (seconds) in JVM lookups. > > OpenJDK issues document repeated timeouts and lack of > > effective caching paths for some rDNS calls. Putting rDNS in critical > paths > > (TLS, handshake, request handling) can amplify random outages. > > > > All in all I'm not yet convinced that this issue appears in other > trending > > environments like k8s. > > Adding this together with the mentioned risks I personally wouldn't > merge > > it to the main repo. > > > > BR, > > G > > > > [1] https://cwe.mitre.org/data/definitions/350.html > > > > > > On Fri, Aug 15, 2025 at 7:44 PM Yaroslav Chernysh <ya...@gmail.com> > > wrote: > > > > > Hi Gobor, > > > > > > Thank you for such a quick response, I appreciate it. > > > > > > Actually, I'm not very good at all this security and networking > stuff, so > > > I apologize in advance if I'm wrong in some statement. > > > > > > > Does YARN containers share the host’s network in your case? > > > > > > Yes, it does. And as far as I have researched, it always does, > possibly > > > only unless you have configured YARN to use Docker containers > > > > < > https://hadoop.apache.org/docs/r3.4.1/hadoop-yarn/hadoop-yarn-site/DockerContainers.html > >, > > > which is definitely not my case. I have also done some testing on > my node, > > > which has 2 IP addresses: > > > > > > - With default rest.bind-address (set by YARN to Node Manager's > hostname), > > > the only IP address that opens a port is the one that NM hostname is > > > resolved to. The other one (not sure where it comes from, this is a > VM) > > > remains closed > > > > > > - With rest.bind-address set to 0.0.0.0, the port is open and > accessible > > > via both IP addresses > > > > > > > However if you have a single IP then using 0.0.0.0 and binding it to > > > lo + eth0 is something what I wouldn't worry about. > > > > > > I got the point and basically I agree here, but I'm not sure how > > > future-proof this approach is. How probable is a scenario in which the > > > environment (single IP node) is changed (to a multi-homed node), but > > > unchanged configuration (still listening on 0.0.0.0) now leads to an > > > excessive network exposure? Either way, that's not my case. And I > think > > > this is not restricted to YARN too: binding to all interfaces in > Standalone > > > deployment might be too excessive as well. > > > > > > > but you still have control on firewall, right? > > > > > > Probably yes (saying for an average user). This would probably > cover the > > > excessive binding leak, however only at the firewall level and not > at the > > > "core". This adds a dependency on firewall. I'm not saying it's > bad, but > > > rather that using the defense-in-depth approach and doing both limited > > > binding and adding firewall would be even better than relying on > firewall > > > only. > > > > > > I hope all the above proves the point that even with good enough > > > environment (number of IP address + firewall) it still does make > sense to > > > restrict the binding. At least that's how I see this, please > correct me if > > > I'm wrong. > > > > > > > introduce reverse DNS lookup as a must have feature > > > > > > Could we make it optional and disabled by default? > > > > > > Thanks, > > > > > > Yaroslav > > > > > > On 2025/08/14 21:32:40 Gabor Somogyi wrote: > > > > Hi Yaroslav, > > > > > > > > First of all I would like to understand why you think binding to > 0.0.0.0 > > > is > > > > less secure in your case. Correct me if I'm wrong: > > > > Does YARN containers share the host’s network in your case? On a > > > > multi-homed node, 0.0.0.0 exposes on every host interface, > > > > which can be less secure than binding to a specific host IP. So > this case > > > > pinning can matter. > > > > > > > > However if you have a single IP then using 0.0.0.0 and binding it > to lo + > > > > eth0 is something what I wouldn't worry about. > > > > Like a "normal" kubernetes pod (default networking, single > interface, no > > > > hostNetwork) has no such issue. > > > > > > > > As a general remark. Let's say you expose the REST endpoint on 2 IP > > > > addresses but you still have control on firewall, right? > > > > > > > > The main reason why I'm asking these questions is because using > > > > `getHostName` would introduce reverse DNS lookup as a must have > feature. > > > > That could cause quite some turbulences at heavy users by additional > > > > traffic, PTR records can be wrong or spoofed, etc... > > > > > > > > BR, > > > > G > > > > > > > > > > > > On Thu, Aug 14, 2025 at 8:13 PM Yaroslav Chernysh <ya...@gmail.com> > > > <ya...@gmail.com> > > > > wrote: > > > > > > > > > Hi Flink community, > > > > > > > > > > Is there a particular reason to advertise Job Manager's REST > endpoint > > > > > address in a form of IP address instead of hostname? More > precisely, > > > I'm > > > > > talking about this code block > > > > > > > > > < > https://github.com/apache/flink/blob/release-2.0.0/flink-runtime/src/main/java/org/apache/flink/runtime/rest/RestServerEndpoint.java#L298-L304 > > > > > > < > https://github.com/apache/flink/blob/release-2.0.0/flink-runtime/src/main/java/org/apache/flink/runtime/rest/RestServerEndpoint.java#L298-L304 > > > > > in > > > > > RestServerEndpoint.java: > > > > > > > > > > final InetSocketAddress bindAddress = (InetSocketAddress) > > > > > serverChannel.localAddress(); > > > > > final String advertisedAddress; > > > > > if (bindAddress.getAddress().isAnyLocalAddress()) { > > > > > advertisedAddress = this.restAddress; > > > > > } else { > > > > > advertisedAddress = > > > > > bindAddress.getAddress().getHostAddress(); > > > > > } > > > > > > > > > > That is (as far as I understood), if rest.bind-address is set > to the > > > > > 0.0.0.0 wildcard (which means binding to all available > interfaces), > > > then > > > > > the advertised address will be the value of rest.address. > Otherwise, an > > > > > address in a form of IP address of the specified rest.bind-address > > > will be > > > > > used. > > > > > What if I want to bind the REST endpoint to some specific > address (for > > > > > security reasons), but at the same time advertise it in the form > of > > > > > hostname? Assuming that all the name resolution things work > correctly. > > > > > > > > > > For me particularly, the problem this creates is with SSL. The > > > certificate > > > > > I have for the Job Manager (REST connectivity) is created with a > > > hostname > > > > > and not an IP address. I run Flink on YARN and this way the > default > > > value > > > > > for rest.bind-address is Node Manager's hostname (thus, not the > 0.0.0.0 > > > > > wildcard), and the same goes for rest.address. This way, the > advertised > > > > > address is in the form of an IP address. I'd like to access > Flink's UI > > > via > > > > > the YARN Resource Manager proxy ("Tracking URL" in the application > > > page) > > > > > that has the Job Manager's certificate in its truststore. > However, due > > > to > > > > > the Flink being advertised to Resource Manager with the IP > address and > > > the > > > > > certificate holds the hostname, the connection from Resource > Manager > > > to Job > > > > > Manager fails with: > > > > > > > > > > javax.net.ssl.SSLPeerUnverifiedException: Certificate for > > > <192.168.33.11> > > > > > doesn't match any of the subject alternative names: [] > > > > > > > > > > The only way I can fix this (without code changes) is by > explicitly > > > > > setting rest.bind-address to 0.0.0.0, which is not secure, as > far as I > > > > > understand (less secure than binding to a specific address). > > > > > However, if I substitute the getHostAddress() call in the code > block > > > above > > > > > with the getHostName(), the issue is gone. > > > > > > > > > > So, my question is: is there any particular reason not to > > > > > use getHostName() here (assuming hostname is available)? > > > > > > > > > > Thanks, > > > > > Yaroslav > > > > > > > > > > > > > > >
