Polling the Ambari server via REST (or their API if they have one), would entail all workers hitting one server and create a single point of failure (the ambari server is what serves up REST). Zookeeper's intent is to not have a single point of failure like this and (one of its main) use-cases is to serve up configs in a distributed environment.
Casey On Fri, Jan 13, 2017 at 9:55 AM, Nick Allen <n...@nickallen.org> wrote: > Let me ask a stupid question. What does Zookeeper do for us that Ambari > cannot? Why keep Zookeeper in the mix? > > > > On Fri, Jan 13, 2017 at 9:28 AM, David Lyle <dlyle65...@gmail.com> wrote: > > > In the main yes- I've made some changes: > > > > - Expand ambari to manage the remaining sensor-specific configs > > - Refactor the push calls to zookeeper (in ConfigurationUtils, I think) > > to push to ambari and take an Ambari user/pw and (optionally) reason > > - (Ambari can push to zookeeper, but it requires a service restart, so > for > > "live changes" you may > > want do both a rest call and zookeeper update from > ConfigurationUtils) > > WAS > > Question remains about whether ambari can do the push to zookeeper > > or whetheror whether ConfigurationUtils has to push to zookeeper as > > well as update > > ambari. > > - Refactor the middleware that Ryan submitted to have the API calls > take > > an Ambari user/pw and (optionally) reason > > - Refactor the management UI to pass in an Ambari user/pw and > > (optionally) reason > > - Refactor the Stellar Management functions CONFIG_PUT to accept an > > Ambari user/pw and (optionally) reason > > > > I think we'd need to do some detailed design around how to handle what we > > expect to be dynamic configs, but the main principle should (imo) be to > > always know who and why and make sure that Ambari is aware and is the > > static backing store for Zookeeper. > > > > -D... > > > > > > On Fri, Jan 13, 2017 at 9:19 AM, Casey Stella <ceste...@gmail.com> > wrote: > > > > > So, basically, your proposed changes, broken into tangible gobbets of > > work: > > > > > > - Expand ambari to manage the remaining sensor-specific configs > > > - Refactor the push calls to zookeeper (in ConfigurationUtils, I > > think) > > > to push to ambari and take a reason > > > - Question remains about whether ambari can do the push to > > zookeeper > > > or whether ConfigurationUtils has to push to zookeeper as well as > > > update > > > ambari. > > > - Refactor the middleware that Ryan submitted to have the API calls > > take > > > a reason > > > - Refactor the management UI to pass in a reason > > > - Refactor the Stellar Management functions CONFIG_PUT to accept a > > > reason > > > > > > Just so we can evaluate it and I can ensure I haven't overlooked some > > > important point. Please tell me if Ambari cannot do the things we're > > > suggesting it can do. > > > > > > Casey > > > > > > On Fri, Jan 13, 2017 at 9:15 AM, David Lyle <dlyle65...@gmail.com> > > wrote: > > > > > > > That's exactly correct, Casey. Basically, an expansion of what we're > > > > currently doing with global.json, enrichment.properties and > > > > elasticsearch.properties. > > > > > > > > -D... > > > > > > > > > > > > On Fri, Jan 13, 2017 at 9:12 AM, Casey Stella <ceste...@gmail.com> > > > wrote: > > > > > > > > > I would suggest not having Ambari replace zookeeper. I think the > > > > proposal > > > > > is to have Ambari replace the editable store (like the JSON files > on > > > > > disk). Zookeeper woudl be the source of truth for the running > > > topologies > > > > > and ambari would be sync'd to it. > > > > > > > > > > Correct if I misspeak, dave or matt. > > > > > > > > > > Casey > > > > > > > > > > On Fri, Jan 13, 2017 at 9:09 AM, Nick Allen <n...@nickallen.org> > > > wrote: > > > > > > > > > > > Ambari seems like a logical choice. > > > > > > > > > > > > *>> It doesn’t natively integrate Zookeeper storage of configs, > but > > > > there > > > > > > is a natural place to specify copy to/from Zookeeper for the > files > > > > > > desired.* > > > > > > > > > > > > How would Ambari interact with Zookeeper in this scenario? Would > > > > Ambari > > > > > > replace Zookeeper completely? Or would Zookeeper act as the > > > persistence > > > > > > tier under Ambari? > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > On Thu, Jan 12, 2017 at 9:24 PM, Matt Foley <ma...@apache.org> > > > wrote: > > > > > > > > > > > > > Mike, could you try again on the image, please, making sure it > > is a > > > > > > simple > > > > > > > format (gif, png, or jpeg)? It got munched, at least in my > > viewer. > > > > > > Thanks. > > > > > > > > > > > > > > Casey, responding to some of the questions you raised: > > > > > > > > > > > > > > I’m going to make a rather strong statement: We already have a > > > > service > > > > > > > “to intermediate and handle config update/retrieval”. > > > > > > > Furthermore, it: > > > > > > > - Correctly handles the problems of distributed services > running > > on > > > > > > > multi-node clusters. (That’s a HARD problem, people, and we > > > > shouldn’t > > > > > > try > > > > > > > to reinvent the wheel.) > > > > > > > - Correctly handles Kerberos security. (That’s kinda hard too, > or > > > at > > > > > > least > > > > > > > a lot of work.) > > > > > > > - It does automatic versioning of configurations, and allows > > > viewing, > > > > > > > comparing, and reverting historical configs > > > > > > > - It has a capable REST API for all those things. > > > > > > > It doesn’t natively integrate Zookeeper storage of configs, but > > > there > > > > > is > > > > > > a > > > > > > > natural place to specify copy to/from Zookeeper for the files > > > > desired. > > > > > > > > > > > > > > It is Ambari. And we should commit to it, rather than try to > > > > re-create > > > > > > > such features. > > > > > > > Because it has a good REST API, it is perfectly feasible to > > > implement > > > > > > > Stellar functions that call it. > > > > > > > GUI configuration tools can also use the Ambari APIs, or better > > yet > > > > be > > > > > > > integrated in an “Ambari View”. (Eg, see the “Yarn Capacity > > > Scheduler > > > > > > > Configuration Tool” example in the Ambari documentation, under > > > “Using > > > > > > > Ambari Views”.) > > > > > > > > > > > > > > Arguments are: Parsimony, Sufficiency, Not reinventing the > wheel, > > > and > > > > > Not > > > > > > > spending weeks and weeks of developer time over the next year > > > > > reinventing > > > > > > > the wheel while getting details wrong multiple times… > > > > > > > > > > > > > > Okay, off soapbox. > > > > > > > > > > > > > > Casey asked what the config update behavior of Ambari is, and > how > > > it > > > > > will > > > > > > > interact with changes made from outside Ambari. > > > > > > > The following is from my experience working with the Ambari > Mpack > > > for > > > > > > > Metron. I am not otherwise an Ambari expert, so tomorrow I’ll > > get > > > it > > > > > > > reviewed by an Ambari development engineer. > > > > > > > > > > > > > > Ambari-server runs on one node, and Ambari-agent runs on each > of > > > all > > > > > the > > > > > > > nodes. > > > > > > > Ambari-server has a private set of py, xml, and template files, > > > which > > > > > > > together are used both to generate the Ambari configuration > GUI, > > > with > > > > > > > defaults, and to generate configuration files (of any needed > > > > filetype) > > > > > > for > > > > > > > the various Stack components. > > > > > > > Ambari-server also has a database where it stores the schema > > > related > > > > to > > > > > > > these files, so even if you reach in and edit Ambari’s files, > it > > > will > > > > > > Error > > > > > > > out if the set of parameters or parameter names changes. The > > > > > historical > > > > > > > information about configuration changes is also stored in the > db. > > > > > > > For each component (and in the case of Metron, for each > > topology), > > > > > there > > > > > > > is a python file which controls the logic for these actions, > > among > > > > > > others: > > > > > > > - Install > > > > > > > - Start / stop / restart / status > > > > > > > - Configure > > > > > > > > > > > > > > It is actually up to this python code (which we wrote for the > > > Metron > > > > > > > Mpack) what happens in each of these API calls. But the > current > > > > code, > > > > > > and > > > > > > > I believe this is typical of Ambari-managed components, > performs > > a > > > > > > > “Configure” action whenever you press the “Save” button after > > > > changing > > > > > a > > > > > > > component config in Ambari, and also on each Install and Start > or > > > > > > Restart. > > > > > > > > > > > > > > The Configure action consists of approximately the following > > > sequence > > > > > > (see > > > > > > > disclaimer above :-) > > > > > > > - Recreate the generated config files, using the template files > > and > > > > the > > > > > > > actual configuration most recently set in Ambari > > > > > > > o Note this is also under the control of python code that we > > wrote, > > > > and > > > > > > > this is the appropriate place to push to ZK if desired. > > > > > > > - Propagate those config files to each Ambari-agent, with a > > command > > > > to > > > > > > set > > > > > > > them locally > > > > > > > - The ambari-agents on each node receive the files and write > them > > > to > > > > > the > > > > > > > specified locations on local storage > > > > > > > > > > > > > > Ambari-server then whines that the updated services should be > > > > > restarted, > > > > > > > but does not initiate that action itself (unless of course the > > > > > initiating > > > > > > > action was a Start command from the administrator). > > > > > > > > > > > > > > Make sense? It’s all quite straightforward in concept, there’s > > > just > > > > an > > > > > > > awful lot of stuff wrapped around that to make it all go > smoothly > > > and > > > > > > > handle the problems when it doesn’t. > > > > > > > > > > > > > > There’s additional complexity in that the Ambari-agent also > > caches > > > > (on > > > > > > > each node) both the template files and COMPILED forms of the > > python > > > > > files > > > > > > > (.pyc) involved in transforming them. The pyc files > incorporate > > > some > > > > > > > amount of additional info regarding parameter values, but I’m > not > > > > sure > > > > > of > > > > > > > the form. I don’t think that changes the above in any > practical > > > way > > > > > > unless > > > > > > > you’re trying to cheat Ambari by reaching in and editing its > > files > > > > > > > directly. In that case, you also need to whack the pyc files > (on > > > > each > > > > > > > node) to force the data to be reloaded from Ambari-server. > Best > > > > > solution > > > > > > > is don’t cheat. > > > > > > > > > > > > > > Also, there may be circumstances under which the Ambari-agent > > will > > > > > detect > > > > > > > changes and re-write the latest version it knows of the config > > > files, > > > > > > even > > > > > > > without a Save or Start action at the Ambari-server. I’m not > > sure > > > of > > > > > > this > > > > > > > and need to check with Ambari developers. It may no longer > > happen, > > > > > altho > > > > > > > I’m pretty sure change detection/reversion was a feature of > early > > > > > > versions > > > > > > > of Ambari. > > > > > > > > > > > > > > Hope this helps, > > > > > > > --Matt > > > > > > > > > > > > > > ================================================ > > > > > > > From: Michael Miklavcic <michael.miklav...@gmail.com> > > > > > > > Reply-To: "dev@metron.incubator.apache.org" > > > > > > <dev@metron.incubator.apache. > > > > > > > org> > > > > > > > Date: Thursday, January 12, 2017 at 3:59 PM > > > > > > > To: "dev@metron.incubator.apache.org" > > > <dev@metron.incubator.apache. > > > > org > > > > > > > > > > > > > Subject: Re: [DISCUSS] Ambari Metron Configuration Management > > > > > > consequences > > > > > > > and call to action > > > > > > > > > > > > > > Hi Casey, > > > > > > > > > > > > > > Thanks for starting this thread. I believe you are correct in > > your > > > > > > > assessment of the 4 options for updating configs in Metron. > When > > > > using > > > > > > more > > > > > > > than one of these options we can get into a split-brain > > scenario. A > > > > > basic > > > > > > > example is updating the global config on disk and using the > > > > > > > zk_load_configs.sh. Later, if a user decides to restart Ambari, > > the > > > > > > cached > > > > > > > version stored by Ambari (it's in the MySQL or other database > > > backing > > > > > > > Ambari) will be written out to disk in the defined config > > > directory, > > > > > and > > > > > > > subsequently loaded using the zk_load_configs.sh under the > hood. > > > Any > > > > > > global > > > > > > > configuration modified outside of Ambari will be lost at this > > > point. > > > > > This > > > > > > > is obviously undesirable, but I also like the purpose and > utility > > > > > exposed > > > > > > > by the multiple config management interfaces we currently have > > > > > > available. I > > > > > > > also agree that a service would be best. > > > > > > > > > > > > > > For reference, here's my understanding of the current > > configuration > > > > > > > loading mechanisms and their deps. > > > > > > > > > > > > > > <image> > > > > > > > > > > > > > > Mike > > > > > > > > > > > > > > > > > > > > > On Thu, Jan 12, 2017 at 3:08 PM, Casey Stella < > > ceste...@gmail.com> > > > > > > wrote: > > > > > > > > > > > > > > In the course of discussion on the PR for METRON-652 > > > > > > > <https://github.com/apache/incubator-metron/pull/415> > something > > > > that I > > > > > > > should definitely have understood better came to light and I > > > thought > > > > > that > > > > > > > it was worth bringing to the attention of the community to get > > > > > > > clarification/discuss is just how we manage configs. > > > > > > > > > > > > > > Currently (assuming the management UI that Ryan Merriman > > submitted) > > > > > > configs > > > > > > > are managed/adjusted via a couple of different mechanism. > > > > > > > > > > > > > > - zk_load_utils.sh: pushed and pulled from disk to zookeeper > > > > > > > - Stellar REPL: pushed and pulled via the > > CONFIG_GET/CONFIG_PUT > > > > > > > functions > > > > > > > - Ambari: initialized via the zk_load_utils script and then > > some > > > > of > > > > > > them > > > > > > > are managed directly (global config) and some indirectly > > > > > > > (sensor-specific > > > > > > > configs). > > > > > > > - NOTE: Upon service restart, it may or may not overwrite > > > > changes > > > > > > on > > > > > > > disk or on zookeeper. *Can someone more knowledgeable > than > > > me > > > > > > about > > > > > > > this describe precisely the semantics that we can expect > on > > > > > > > service restart > > > > > > > for Ambari? What gets overwritten on disk and what gets > > > updated > > > > > > > in ambari?* > > > > > > > - The Management UI: manages some of the configs. *RYAN: > Which > > > > > configs > > > > > > > do we support here and which don't we support here?* > > > > > > > > > > > > > > As you can see, we have a mishmash of mechanisms to update and > > > manage > > > > > the > > > > > > > configuration for Metron in zookeeper. In the beginning the > > > approach > > > > > was > > > > > > > just to edit configs on disk and push/pull them via > > zk_load_utils. > > > > > > Configs > > > > > > > could be historically managed using source control, etc. As we > > got > > > > > more > > > > > > > and more components managing the configs, we haven't taken care > > > that > > > > > they > > > > > > > they all work with each other in an expected way (I believe > these > > > are > > > > > > > true..correct me if I'm wrong): > > > > > > > > > > > > > > - If configs are modified in the management UI or the > Stellar > > > REPL > > > > > and > > > > > > > someone forgets to pull the configs from zookeeper to disk, > > > before > > > > > > they > > > > > > > do > > > > > > > a push via zk_load_utils, they will clobber the configs in > > > > zookeeper > > > > > > > with > > > > > > > old configs. > > > > > > > - If the global config is changed on disk and the ambari > > service > > > > > > > restarts, it'll get reset with the original global config. > > > > > > > - *Ryan, in the management UI, if someone changes the > > zookeeper > > > > > > configs > > > > > > > from outside, are those configs reflected immediately in the > > > UI?* > > > > > > > > > > > > > > > > > > > > > It seems to me that we have a couple of options here: > > > > > > > > > > > > > > - A service to intermediate and handle config > update/retrieval > > > and > > > > > > > tracking historical changes so these different mechanisms > can > > > use > > > > a > > > > > > > common > > > > > > > component for config management/tracking and refactor the > > > existing > > > > > > > mechanisms to use that service > > > > > > > - Standardize on exactly one component to manage the configs > > and > > > > > > regress > > > > > > > the others (that's a verb, right? nicer than delete.) > > > > > > > > > > > > > > I happen to like the service approach, myself, but I wanted to > > put > > > it > > > > > up > > > > > > > for discussion and hopefully someone will volunteer to design > > such > > > a > > > > > > thing. > > > > > > > > > > > > > > To frame the debate, I want us to keep in mind a couple of > things > > > > that > > > > > > may > > > > > > > or may not be relevant to the discussion: > > > > > > > > > > > > > > - We will eventually be moving to support kerberos so there > > > should > > > > > at > > > > > > > least be a path to use kerberos for any solution IMO > > > > > > > - There is value in each of the different mechanisms in > place > > > now. > > > > > If > > > > > > > there weren't, then they wouldn't have been created. Before > > we > > > > try > > > > > to > > > > > > > make > > > > > > > this a "there can be only one" argument, I'd like to hear > very > > > > good > > > > > > > arguments. > > > > > > > > > > > > > > Finally, I'd appreciate if some people might answer the > > questions I > > > > > have > > > > > > in > > > > > > > bold there. Hopefully this discussion, if nothing else > happens, > > > will > > > > > > > result in fodder for proper documentation of the ins and outs > of > > > each > > > > > of > > > > > > > the components bulleted above. > > > > > > > > > > > > > > Best, > > > > > > > > > > > > > > Casey > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > -- > > > > > > Nick Allen <n...@nickallen.org> > > > > > > > > > > > > > > > > > > > > > > > > -- > Nick Allen <n...@nickallen.org> >
