1. TM registers at RM 2. JobMaster requests slot from RM -> TM gets notified 3. JM fails over 4. TM re-offers the slot to the failed over JobMaster 5. TM reconnects to RM at some point
Here's an example for the TM to run workloads without being connected to the RM, without ever having a valid token:
1. TM1 has a valid token and is running some tasks. 2. TM1 crashes 3. TM2 is started to take over, and re-uses the working directory of TM1 (new feature in 1.15!) 4. TM2 recovers the previous slot allocations 5. TM2 is informed about leading JM 6. TM2 starts registration with RM 7. TM2 offers slots to JobMaster 8. TM2 accepts task submission from JobMaster 9. ...some time later the registration completes... On 03/02/2022 14:24, Gabor Somogyi wrote:
> but it can happen that the JobMaster+TM collaborate to run stuff without the TM being registered at the RMHonestly I'm not educated enough within Flink to give an example to such scenario. Until now I thought JM defines tasks to be done and TM just blindly connects to external systems and does the processing. All in all if external systems can be touched when JM + TM collaboration happens then we need to consider that in the design. Since I don't have an example scenario I don't know what exactly needs to be solved. I think we need an example case to decide whether we face a real issue or the design is not leaking.On Thu, Feb 3, 2022 at 2:12 PM Chesnay Schepler <ches...@apache.org> wrote:> Just to learn something new. I think local recovery is clear to me which is not touching external systems like Kafka or so (correct me if I'm wrong). Is it possible that such case the user code just starts to run blindly w/o JM coordination and connects to external systems to do data processing? Local recovery itself shouldn't touch external systems; the TM cannot just run user-code without the JobMaster being involved, but it can happen that the JobMaster+TM collaborate to run stuff without the TM being registered at the RM. On 03/02/2022 13:48, Gabor Somogyi wrote:> Any error in loading the provider (be it by accident or explicit checks) then is a setup error and we can fail the cluster. Fail fast is a good direction in my view. In Spark I wanted to go to this direction but there were other opinions so there if a provider is not loaded then the workload goes further. Of course the processing will fail if the token is missing... > Requiring HBase (and Hadoop for that matter) to be on the JM system classpath would be a bit unfortunate. Have you considered loading the providers as plugins? Even if it's unfortunate the actual implementation is depending on that already. Moving HBase and/or all token providers into plugins is a possibility. That way if one wants to use a specific provider then a plugin need to be added. If we would like to go to this direction I would do that in a separate FLIP not to have feature creep here. The actual FLIP already covers several thousand lines of code changes. > This is missing from the FLIP. From my experience with the metric reporters, having the implementation rely on the configuration is really annoying for testing purposes. That's why I suggested factories; they can take care of extracting all parameters that the implementation needs, and then pass them nicely via the constructor. ServiceLoader provided services must have a norarg constructor where no parameters can be passed. As a side note testing delegation token providers is pain in the ass and not possible with automated tests without creating a fully featured kerberos cluster with KDC, HDFS, HBase, Kafka, etc.. We've had several tries in Spark but then gave it up because of the complexity and the flakyness of it so I wouldn't care much about unit testing. The sad truth is that most of the token providers can be tested manually on cluster. Of course this doesn't mean that the whole code is not intended to be covered with tests. I mean couple of parts can be automatically tested but providers are not such. > This also implies that any fields of the provider wouldn't inherently have to be mutable. I think this is not an issue. A provider connects to a service, obtains token(s) and then close the connection and never seen the need of an intermediate state. I've just mentioned the singleton behavior to be clear. > One examples is a TM restart + local recovery, where the TM eagerly offers the previous set of slots to the leading JM. Just to learn something new. I think local recovery is clear to me which is not touching external systems like Kafka or so (correct me if I'm wrong). Is it possible that such case the user code just starts to run blindly w/o JM coordination and connects to external systems to do data processing? On Thu, Feb 3, 2022 at 1:09 PM Chesnay Schepler <ches...@apache.org> wrote: 1) The manager certainly shouldn't check for specific implementations. The problem with classpath-based checks is it can easily happen that the provider can't be loaded in the first place (e.g., if you don't use reflection, which you currently kinda force), and in that case Flink can't tell whether the token is not required or the cluster isn't set up correctly. As I see it we shouldn't try to be clever; if the users wants kerberos, then have him enable the providers. Any error in loading the provider (be it by accident or explicit checks) then is a setup error and we can fail the cluster. If we still want to auto-detect whether the provider should be used, note that using factories would make this easier; the factory can check the classpath (not having any direct dependencies on HBase avoids the case above), and the provider no longer needs reflection because it will only be used iff HBase is on the CP. Requiring HBase (and Hadoop for that matter) to be on the JM system classpath would be a bit unfortunate. Have you considered loading the providers as plugins? 2) > DelegationTokenProvider#init method This is missing from the FLIP. From my experience with the metric reporters, having the implementation rely on the configuration is really annoying for testing purposes. That's why I suggested factories; they can take care of extracting all parameters that the implementation needs, and then pass them nicely via the constructor. This also implies that any fields of the provider wouldn't inherently have to be mutable. > workloads are not yet running until the initial token set is not propagated. This isn't necessarily true. It can happen that tasks are being deployed to the TM without it having registered with the RM; there is currently no requirement that a TM must be registered before it may offer slots / accept task submissions. One examples is a TM restart + local recovery, where the TM eagerly offers the previous set of slots to the leading JM. On 03/02/2022 12:39, Gabor Somogyi wrote:Thanks for the quick response! Appreciate your invested time... G On Thu, Feb 3, 2022 at 11:12 AM Chesnay Schepler <ches...@apache.org> wrote: Thanks for answering the questions! 1) Does the HBase provider require HBase to be on the classpath? To be instantiated no, to obtain a token yes. If so, then could it even be loaded if Hbase is on the classpath? The provider can be loaded but inside the provider it would detect whether HBase is on classpath. Just to be crystal clear here this is the actual implementation what I would like to take over into the Provider. Please see: https://github.com/apache/flink/blob/e6210d40491ff28c779b8604e425f01983f8a3d7/flink-yarn/src/main/java/org/apache/flink/yarn/Utils.java#L243-L254 I've considered to load only the necessary Providers but that would mean a generic Manager need to know that if the newly loaded Provider is instanceof HBaseDelegationTokenProvider, then it need to be skipped. I think it would add unnecessary complexity to the Manager and it would contain ugly code parts(at least in my view ugly), like this if (provider instanceof HBaseDelegationTokenProvider && hbaseIsNotOnClasspath()) { // Skip intentionally } else if (provider instanceof SomethingElseDelegationTokenProvider && somethingElseIsNotOnClasspath()) { // Skip intentionally } else { providers.put(provider.serviceName(), provider); } I think the least code and most clear approach is to load the providers and decide inside whether everything is given to obtain a token. If not, then you're assuming the classpath of the JM/TM to be the same, which isn't necessarily true (in general; and also if Hbase is loaded from the user-jar). I'm not assuming that the classpath of JM/TM must be the same. If the HBase jar is coming from the user-jar then the HBase code is going to use UGI within the JVM when authentication required. Of course I've not yet tested within Flink but in Spark it is working fine. All in all JM/TM classpath may be different but on both side HBase jar must exists somehow. 2) None of the /Providers/ in your PoC get access to the configuration. Only the /Manager/ is. Note that I do not know whether there is a need for the providers to have access to the config, as that's very implementation specific I suppose. You're right. Since this is just a POC and I don't have green light I've not put too many effort for a proper self-review. DelegationTokenProvider#init method must get Flink configuration. The reason behind is that several further configuration can be find out using that. A good example is to get Hadoop conf. The rationale behind is the same just like before, it would be good to create a generic Manager as possible. To be more specific some code must load Hadoop conf which could be the Manager or the Provider. If the manager does that then the generic Manager must be modified all the time when something special thing is needed for a new provider. This could be super problematic when a custom provider is written. 10) I'm not sure myself. It could be something as trivial as creating some temporary directory in HDFS I suppose. I've not found of such task.YARN and K8S are not expecting such things from executors and workloads are not yet running until the initial token set is not propagated. On 03/02/2022 10:23, Gabor Somogyi wrote:Please see my answers inline. Hope provided satisfying answers to all questions. G On Thu, Feb 3, 2022 at 9:17 AM Chesnay Schepler<ches...@apache.org> <mailto:ches...@apache.org> wrote:I have a few question that I'd appreciate if you could answer them. 1. How does the Provider know whether it is required or not? All registered providers which are registered properly are going to beloaded and asked to obtain tokens. Worth to mention every provider has the right to decide whether it wants to obtain tokens or not (bool delegationTokensRequired()). For instance if provider detects that HBase is not on classpath or not configured properly then no tokens are obtained from that specific provider. You may ask how a provider is registered. Here it is: The provider is on classpath + there is a META-INF file which contains the name of the provider, for example: META-INF/services/org.apache.flink.runtime.security.token.DelegationTokenProvider <https://github.com/apache/flink/compare/master...gaborgsomogyi:dt?expand=1#diff-b65ee7e64c5d2dfbb683d3569fc3e42f4b5a8052ab83d7ac21de5ab72f428e0b> <https://github.com/apache/flink/compare/master...gaborgsomogyi:dt?expand=1#diff-b65ee7e64c5d2dfbb683d3569fc3e42f4b5a8052ab83d7ac21de5ab72f428e0b>1. How does the configuration of Providers work (how do they get access to a configuration)? Flink configuration is going to be passed to all providers. Please see thePOC here: https://github.com/apache/flink/compare/master...gaborgsomogyi:dt?expand=1 Service specific configurations are loaded on-the-fly. For example in HBase case it looks for HBase configuration class which will be instantiated within the provider.1. How does a user select providers? (Is it purely based on the provider being on the classpath?) Providers can be explicitly turned off with the following config:"security.kerberos.tokens.${name}.enabled". I've never seen that 2 different implementation would exist for a specific external service, but if this edge case would exist then the mentioned config need to be added, a new provider with a different name need to be implemented and registered. All in all we've seen that provider handling is not user specific task but a cluster admin one. If a specific provider is needed then it's implemented once per company, registered once to the clusters and then all users may or may not use the obtained tokens. Worth to mention the system will know which token need to be used when HDFS is accessed, this part is automatic.1. How can a user override an existing provider? Pease see the previous bulletpoint. 1. What is DelegationTokenProvider#name() used for? By default all providers which are registered properly (on classpath +META-INF entry) are on by default. With "security.kerberos.tokens.${name}.enabled" a specific provider can be turned off. Additionally I'm intended to use this in log entries later on for debugging purposes. For example "hadoopfs provider obtained 2 tokens with ID...". This would help what and when is happening with tokens. The same applies to TaskManager side: "2 hadoopfs provider tokens arrived with ID...". Important to note that the secret part will be hidden in the mentioned log entries to keep the attach surface low.1. What happens if the names of 2 providers are identical? Presume you mean 2 different classes which both registered and having thesame logic inside. This case both will be loaded and both is going to obtain token(s) for the same service. Both obtained token(s) are going to be added to the UGI. As a result the second will overwrite the first but the order is not defined. Since both token(s) are valid no matter which one is used then access to the external system will work. When the class names are same then service loader only loads a single entry because services are singletons. That's the reason why state inside providers are not advised.1. Will we directly load the provider, or first load a factory (usually preferable)? Intended to load a provider directly by DTM. We can add an extra layer tohave factory but after consideration I came to a conclusion that it would be and overkill this case. Please have a look how it's planned to load providers now: https://github.com/apache/flink/compare/master...gaborgsomogyi:dt?expand=1#diff-d56a0bc77335ff23c0318f6dec1872e7b19b1a9ef6d10fff8fbaab9aecac94faR54-R811. What is the Credentials class (it would necessarily have to be a public api as well)? Credentials class is coming from Hadoop. My main intention was not to bindthe implementation to Hadoop completely. It is not possible because of the following reasons: * Several functionalities are must because there are no alternatives, including but not limited to login from keytab, proper TGT cache handling, passing tokens to Hadoop services like HDFS, HBase, Hive, etc. * The partial win is that the whole delegation token framework is going to be initiated if hadoop-common is on classpath (Hadoop is optional in core libraries) The possibility to eliminate Credentials from API could be: * to convert Credentials to byte array forth and back while a provider gives back token(s): I think this would be an overkill and would make the API less clear what to give back what Manager understands * to re-implement Credentials internal structure in a POJO, here the same convert forth and back would happen between provider and manager. I think this case would be the re-invent the wheel scenario1. What does the TaskManager do with the received token? Puts the tokens into the UserGroupInformation instance for the currentuser. Such way Hadoop compatible services can pick up the tokens from there properly. This is an existing pattern inside Spark.1. Is there any functionality in the TaskManager that could require a token on startup (i.e., before registering with the RM)? Never seen such functionality in Spark and after analysis not seen inFlink too. If you have something in mind which I've missed plz help me out. On 11/01/2022 14:58, Gabor Somogyi wrote:Hi All, Hope all of you have enjoyed the holiday season. I would like to start the discussion on FLIP-211<https://cwiki.apache.org/confluence/display/FLINK/FLIP-211%3A+Kerberos+delegation+token+framework> <https://cwiki.apache.org/confluence/display/FLINK/FLIP-211%3A+Kerberos+delegation+token+framework> <https://cwiki.apache.org/confluence/display/FLINK/FLIP-211%3A+Kerberos+delegation+token+framework> <https://cwiki.apache.org/confluence/display/FLINK/FLIP-211%3A+Kerberos+delegation+token+framework> which aims to provide a Kerberos delegation token framework that /obtains/renews/distributes tokens out-of-the-box. Please be aware that the FLIP wiki area is not fully done since the discussion may change the feature in major ways. The proposal can be found in a google doc here<https://docs.google.com/document/d/1JzMbQ1pCJsLVz8yHrCxroYMRP2GwGwvacLrGyaIx5Yc/edit?fbclid=IwAR0vfeJvAbEUSzHQAAJfnWTaX46L6o7LyXhMfBUCcPrNi-uXNgoOaI8PMDQ> <https://docs.google.com/document/d/1JzMbQ1pCJsLVz8yHrCxroYMRP2GwGwvacLrGyaIx5Yc/edit?fbclid=IwAR0vfeJvAbEUSzHQAAJfnWTaX46L6o7LyXhMfBUCcPrNi-uXNgoOaI8PMDQ> <https://docs.google.com/document/d/1JzMbQ1pCJsLVz8yHrCxroYMRP2GwGwvacLrGyaIx5Yc/edit?fbclid=IwAR0vfeJvAbEUSzHQAAJfnWTaX46L6o7LyXhMfBUCcPrNi-uXNgoOaI8PMDQ> <https://docs.google.com/document/d/1JzMbQ1pCJsLVz8yHrCxroYMRP2GwGwvacLrGyaIx5Yc/edit?fbclid=IwAR0vfeJvAbEUSzHQAAJfnWTaX46L6o7LyXhMfBUCcPrNi-uXNgoOaI8PMDQ> . As the community agrees on the approach the content will be moved to the wiki page. Feel free to add your thoughts to make this feature better! BR, G
