Just piling on in support for Ambari. I really, really don't like reinventing wheels, especially hard ones. I guess my questions now are mainly around technical feasibility. Seems to me that we can either:
- retrofit the tooling that currently manages configs to use the Ambari API's as well as pushing to zokeeper - have a service listening to zookeeper and pushing changes to ambari to keep it in sync - Something that I may have missed Each of those have pro's and con's. Thoughts? Casey On Fri, Jan 13, 2017 at 8:53 AM, David Lyle <dlyle65...@gmail.com> wrote: > I'm in complete agreement with all the points Matt made. I think the way > forward should be to expose ALL user-modifiable configs via Ambari and let > Ambari actively manage them. We should keep the command line tools as the > backend and Ambari should continue to leverage them. This will allow manual > installation/management if desired and will ensure the command line scripts > are kept up to date. > > Fully leveraging Ambari has many beneficial effects. My top four: > Provides proper revision control for the configurations > Scales easily into things like rolling|quick upgrades and Kerberos > support > Provides other applications a restful endpoint to change configurations > We get a force multiplier from the Ambari devs > > The working description Matt provided is completely consistent with my > understanding of how it works (derived from the Ambari docs, authoring > pieces of the mpack and interacting with some Ambari devs). Restarting > Ambari agent is the only circumstance I'm aware of outside of > save/start|restart that would initiate a re-write of the configs and cache, > there could be others. > > -D... > > 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 > > > > > > > > > > > > >
