Ashish, 3. Just want to clarify. Why can't you store ZK connection config in ZK? This is a property for ZK clients, not ZK server.
Thanks, Jun On Wed, May 6, 2015 at 5:48 PM, Ashish Singh <asi...@cloudera.com> wrote: > I too would like to share some concerns that we came up with while > discussing the effect of moving configs to zookeeper will have. > > 1. Kafka will start to become a configuration management tool to some > degree, and be subject to all the things such tools are commonly asked to > do. Kafka'll likely need to re-implement the role / group / service > hierarchy that CM uses. Kafka'll need some way to conveniently dump its > configs so they can be re-imported later, as a backup tool. People will > want this to be audited, which means you'd need distinct logins for > different people, and user management. You can try to push some of this > stuff onto tools like CM, but this is Kafka going out of its way to be > difficult to manage, and most projects don't want to do that. Being unique > in how configuration is done is strictly a bad thing for both integration > and usability. Probably lots of other stuff. Seems like a bad direction. > > 2. Where would the default config live? If we decide on keeping the config > files around just for getting the default config, then I think on restart, > the config file will be ignored. This creates an obnoxious asymmetry for > how to configure Kafka the first time and how you update it. You have to > learn 2 ways of making config changes. If there was a mistake in your > original config file, you can't just edit the config file and restart, you > have to go through the API. Reading configs is also more irritating. This > all creates a learning curve for users of Kafka that will make it harder to > use than other projects. This is also a backwards-incompatible change. > > 3. All Kafka configs living in ZK is strictly impossible, since at the very > least ZK connection configs cannot be stored in ZK. So you will have a file > where some values are in effect but others are not, which is again > confusing. Also, since you are still reading the config file on first > start, there are still multiple sources of truth, or at least the > appearance of such to the user. > > On Wed, May 6, 2015 at 5:33 PM, Jun Rao <j...@confluent.io> wrote: > > > One of the Chef users confirmed that Chef integration could still work if > > all configs are moved to ZK. My rough understanding of how Chef works is > > that a user first registers a service host with a Chef server. After > that, > > a Chef client will be run on the service host. The user can then push > > config changes intended for a service/host to the Chef server. The server > > is then responsible for pushing the changes to Chef clients. Chef clients > > support pluggable logic. For example, it can generate a config file that > > Kafka broker will take. If we move all configs to ZK, we can customize > the > > Chef client to use our config CLI to make the config changes in Kafka. In > > this model, one probably doesn't need to register every broker in Chef > for > > the config push. Not sure if Puppet works in a similar way. > > > > Also for storing the configs, we probably can't store the broker/global > > level configs in Kafka itself (e.g. in a special topic). The reason is > that > > in order to start a broker, we likely need to make some broker level > config > > changes (e.g., the default log.dir may not be present, the default port > may > > not be available, etc). If we need a broker to be up to make those > changes, > > we get into this chicken and egg problem. > > > > Thanks, > > > > Jun > > > > On Tue, May 5, 2015 at 4:14 PM, Gwen Shapira <gshap...@cloudera.com> > > wrote: > > > > > Sorry I missed the call today :) > > > > > > I think an additional requirement would be: > > > Make sure that traditional deployment tools (Puppet, Chef, etc) are > still > > > capable of managing Kafka configuration. > > > > > > For this reason, I'd like the configuration refresh to be pretty close > to > > > what most Linux services are doing to force a reload of configuration. > > > AFAIK, this involves handling HUP signal in the main thread to reload > > > configuration. Then packaging scripts can add something nice like > > "service > > > kafka reload". > > > > > > (See Apache web server: > > > https://github.com/apache/httpd/blob/trunk/build/rpm/httpd.init#L101) > > > > > > Gwen > > > > > > > > > On Tue, May 5, 2015 at 8:54 AM, Joel Koshy <jjkosh...@gmail.com> > wrote: > > > > > > > Good discussion. Since we will be talking about this at 11am, I > wanted > > > > to organize these comments into requirements to see if we are all on > > > > the same page. > > > > > > > > REQUIREMENT 1: Needs to accept dynamic config changes. This needs to > > > > be general enough to work for all configs that we envision may need > to > > > > accept changes at runtime. e.g., log (topic), broker, client > (quotas), > > > > etc.. possible options include: > > > > - ZooKeeper watcher > > > > - Kafka topic > > > > - Direct RPC to controller (or config coordinator) > > > > > > > > The current KIP is really focused on REQUIREMENT 1 and I think that > is > > > > reasonable as long as we don't come up with something that requires > > > > significant re-engineering to support the other requirements. > > > > > > > > REQUIREMENT 2: Provide consistency of configs across brokers (modulo > > > > per-broker overrides) or at least be able to verify consistency. > What > > > > this effectively means is that config changes must be seen by all > > > > brokers eventually and we should be able to easily compare the full > > > > config of each broker. > > > > > > > > REQUIREMENT 3: Central config store. Needs to work with plain > > > > file-based configs and other systems (e.g., puppet). Ideally, should > > > > not bring in other dependencies (e.g., a DB). Possible options: > > > > - ZooKeeper > > > > - Kafka topic > > > > - other? E.g. making it pluggable? > > > > > > > > Any other requirements? > > > > > > > > Thanks, > > > > > > > > Joel > > > > > > > > On Tue, May 05, 2015 at 01:38:09AM +0000, Aditya Auradkar wrote: > > > > > Hey Neha, > > > > > > > > > > Thanks for the feedback. > > > > > 1. In my earlier exchange with Jay, I mentioned the broker writing > > all > > > > it's configs to ZK (while respecting the overrides). Then ZK can be > > used > > > to > > > > view all configs. > > > > > > > > > > 2. Need to think about this a bit more. Perhaps we can discuss this > > > > during the hangout tomorrow? > > > > > > > > > > 3 & 4) I viewed these config changes as mainly administrative > > > > operations. In the case, it may be reasonable to assume that the ZK > > port > > > is > > > > available for communication from the machine these commands are run. > > > Having > > > > a ConfigChangeRequest (or similar) is nice to have but having a new > API > > > and > > > > sending requests to controller also change how we do topic based > > > > configuration currently. I was hoping to keep this KIP as minimal as > > > > possible and provide a means to represent and modify client and > broker > > > > based configs in a central place. Are there any concerns if we tackle > > > these > > > > things in a later KIP? > > > > > > > > > > Thanks, > > > > > Aditya > > > > > ________________________________________ > > > > > From: Neha Narkhede [n...@confluent.io] > > > > > Sent: Sunday, May 03, 2015 9:48 AM > > > > > To: dev@kafka.apache.org > > > > > Subject: Re: [DISCUSS] KIP-21 Configuration Management > > > > > > > > > > Thanks for starting this discussion, Aditya. Few questions/comments > > > > > > > > > > 1. If you change the default values like it's mentioned in the KIP, > > do > > > > you > > > > > also overwrite the local config file as part of updating the > default > > > > value? > > > > > If not, where does the admin look to find the default values, ZK or > > > local > > > > > Kafka config file? What if a config value is different in both > > places? > > > > > > > > > > 2. I share Gwen's concern around making sure that popular config > > > > management > > > > > tools continue to work with this change. Would love to see how each > > of > > > > > those would work with the proposal in the KIP. I don't know enough > > > about > > > > > each of the tools but seems like in some of the tools, you have to > > > define > > > > > some sort of class with parameter names as config names. How will > > such > > > > > tools find out about the config values? In Puppet, if this means > that > > > > each > > > > > Puppet agent has to read it from ZK, this means the ZK port has to > be > > > > open > > > > > to pretty much every machine in the DC. This is a bummer and a very > > > > > confusing requirement. Not sure if this is really a problem or not > > > (each > > > > of > > > > > those tools might behave differently), though pointing out that > this > > is > > > > > something worth paying attention to. > > > > > > > > > > 3. The wrapper tools that let users read/change config tools should > > not > > > > > depend on ZK for the reason mentioned above. It's a pain to assume > > that > > > > the > > > > > ZK port is open from any machine that needs to run this tool. > Ideally > > > > what > > > > > users want is a REST API to the brokers to change or read the > config > > > (ala > > > > > Elasticsearch), but in the absence of the REST API, we should think > > if > > > we > > > > > can write the tool such that it just requires talking to the Kafka > > > broker > > > > > port. This will require a config RPC. > > > > > > > > > > 4. Not sure if KIP is the right place to discuss the design of > > > > propagating > > > > > the config changes to the brokers, but have you thought about just > > > > letting > > > > > the controller oversee the config changes and propagate via RPC to > > the > > > > > brokers? That way, there is an easier way to express config changes > > > that > > > > > require all brokers to change it for it to be called complete. > Maybe > > > this > > > > > is not required, but it is hard to say if we don't discuss the full > > set > > > > of > > > > > configs that need to be dynamic. > > > > > > > > > > Thanks, > > > > > Neha > > > > > > > > > > On Fri, May 1, 2015 at 12:53 PM, Jay Kreps <jay.kr...@gmail.com> > > > wrote: > > > > > > > > > > > Hey Aditya, > > > > > > > > > > > > This is a great! A couple of comments: > > > > > > > > > > > > 1. Leaving the file config in place is definitely the least > > > > disturbance. > > > > > > But let's really think about getting rid of the files and just > have > > > one > > > > > > config mechanism. There is always a tendency to make everything > > > > pluggable > > > > > > which so often just leads to two mediocre solutions. Can we do > the > > > > exercise > > > > > > of trying to consider fully getting rid of file config and seeing > > > what > > > > goes > > > > > > wrong? > > > > > > > > > > > > 2. Do we need to model defaults? The current approach is that if > > you > > > > have a > > > > > > global config x it is overridden for a topic xyz by > /topics/xyz/x, > > > and > > > > I > > > > > > think this could be extended to /brokers/0/x. I think this is > > > simpler. > > > > We > > > > > > need to specify the precedence for these overrides, e.g. if you > > > > override at > > > > > > the broker and topic level I think the topic level takes > > precedence. > > > > > > > > > > > > 3. I recommend we have the producer and consumer config just be > an > > > > override > > > > > > under client.id. The override is by client id and we can have > > > separate > > > > > > properties for controlling quotas for producers and consumers. > > > > > > > > > > > > 4. Some configs can be changed just by updating the reference, > > others > > > > may > > > > > > require some action. An example of this is if you want to disable > > log > > > > > > compaction (assuming we wanted to make that dynamic) we need to > > call > > > > > > shutdown() on the cleaner. I think it may be required to > register a > > > > > > listener callback that gets called when the config changes. > > > > > > > > > > > > 5. For handling the reference can you explain your plan a bit? > > > > Currently we > > > > > > have an immutable KafkaConfig object with a bunch of vals. That > or > > > > > > individual values in there get injected all over the code base. I > > was > > > > > > thinking something like this: > > > > > > a. We retain the KafkaConfig object as an immutable object just > as > > > > today. > > > > > > b. It is no longer legit to grab values out fo that config if > they > > > are > > > > > > changeable. > > > > > > c. Instead of making KafkaConfig itself mutable we make > > > > KafkaConfiguration > > > > > > which has a single volatile reference to the current KafkaConfig. > > > > > > KafkaConfiguration is what gets passed into various components. > So > > to > > > > > > access a config you do something like config.instance.myValue. > When > > > the > > > > > > config changes the config manager updates this reference. > > > > > > d. The KafkaConfiguration is the thing that allows doing the > > > > > > configuration.onChange("my.config", callback) > > > > > > > > > > > > -Jay > > > > > > > > > > > > On Tue, Apr 28, 2015 at 3:57 PM, Aditya Auradkar < > > > > > > aaurad...@linkedin.com.invalid> wrote: > > > > > > > > > > > > > Hey everyone, > > > > > > > > > > > > > > Wrote up a KIP to update topic, client and broker configs > > > > dynamically via > > > > > > > Zookeeper. > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > https://cwiki.apache.org/confluence/display/KAFKA/KIP-21+-+Dynamic+Configuration > > > > > > > > > > > > > > Please read and provide feedback. > > > > > > > > > > > > > > Thanks, > > > > > > > Aditya > > > > > > > > > > > > > > PS: I've intentionally kept this discussion separate from KIP-5 > > > > since I'm > > > > > > > not sure if that is actively being worked on and I wanted to > > start > > > > with a > > > > > > > clean slate. > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > -- > > > > > Thanks, > > > > > Neha > > > > > > > > -- > > > > Joel > > > > > > > > > > > > > -- > > Regards, > Ashish >
