jmx-dev JEP review : JDK-8171311 - REST APIs for JMX

Tue Sep 12 10:57:30 UTC 2017

> On Sep 12, 2017, at 12:44 PM, Erik Gahlin <erik.gahlin at oracle.com> wrote:
> 
> I guess there are two use cases:
> 
> 1) Simple interoperability with other languages.
> 2) A drop in replacement for RMI
> 
> Can a JMX connector be written that support both use cases? I don't know, but if not it could be that we need both a connector and an adapter.

I think if you were to extend JMXConnector to wrap the REST API you might be able to expose both. But I’m not sure it would be a great solution. I think a second JEP would be a better option.

— Kirk

> 
> Erik
> 
>> Hi Kirk,
>> 
>> I guess the term 'connector' here is loosely applied. When I say connector, I mean the connector that provides implementation of the package below,
>> 
>> https://docs.oracle.com/javase/8/docs/api/javax/management/remote/package-summary.html <https://docs.oracle.com/javase/8/docs/api/javax/management/remote/package-summary.html>
>> RMIConnector is one implementation of above connector. 
>> 
>> On Tuesday 12 September 2017 12:56 PM, Kirk Pepperdine wrote:
>>> Hi Harsha,
>>> 
>>> From Chapter 5 of the JMX documentation. "Many different implementations of connectors are possible. In particular, there are many possibilities for the protocol used to communicate over a connection between client and server.”
>>> 
>>> It goes on in the Generic Connector section under "User-Defined Protocols” to say; "While the RMI connector must be present in every implementation of the JMX Remote API, you can also implement a connector based on a protocol that is not defined in the JMX Remote API standard. A typical example of this is a connector based on a protocol that uses HTTP/S. Other protocols are also possible. The JMX specification describes how to implement a connector based on a user-defined protocol.”
>>> 
>>> Unless I’m missing something, this all suggests that there is nothing inherently wrong is using REST behind a JMXConnector.
>> I hope above should clarify what I refer to when I say JMXConnector. In that sense, REST APIs alone cannot work as connector. In fact, it stands parallel to connector, as in it directly wraps the MBeanServer and does not wrap any JMXConnector. The JEP has detailed information about where the REST adapter sits in the JMX architecture. 
>> 
>> Are you suggesting that we implement a JMXConnector that works over REST?
>>> 
>>> As written this JEP pretty much looks like Jolokia. Jolokia is a great project and as such I fail to see the benefits of simply duplicating it. I’d also argue that the usefulness of that project has been some what muted because it is not a drop in replacement for the standard RMI connector meaning that one has to modify an entire tool chain just to make use of it. However, creating a REST based JMXConnector would be immediately useful.
>>> As an aside, Jus last week I started on a JMXConnector that uses a shared memory segment for communications. Of course this implementation would only be available for local communications but it offers some advantages over using a socket based protocol, even if that comms is over local loopback.
>>> 
>>> Kind regards,
>>> Kirk Pepperdine
>> 
>> Thanks
>> Harsha
>>> 
>>> 
>>> 
>>>> On Sep 12, 2017, at 9:04 AM, Harsha Wardhana B < <mailto:harsha.wardhana.b at oracle.com>harsha.wardhana.b at oracle.com <mailto:harsha.wardhana.b at oracle.com>> wrote:
>>>> 
>>>> Hi Kirk,
>>>> 
>>>> REST APIs work as an adapter and cannot work as a connector. To quote from the JEP,
>>>> 
>>>> 
>>>>> The REST adapter is a part of the Distributed services level. Connectors mirror the interfaces of agent level services to remote clients, whereas adapters transform agent level services to different protocol. The proposed functionality will transform Agent level services to REST APIs, hence the name "REST adapter".
>>>> A connector *must* adhere to the JMX remoting spec. REST APIs cannot adhere to that because they expose APIs via HTTP and not Java. Hence it is called an Adapter and not a connector. It can never work as a 'drop-in' replacement for JMX/RMI Connector. Existing tools using using RMIConnector will have to be modified to use REST APIs. 
>>>> 
>>>> The current JEP does not allow all of the CRUD operations on MBeans. In the spirit of keeping the APIs language agnostic, only read/write is supported. It is not possible to specify create/delete REST APIs for JMX without incorporating language specific features. I would welcome discussions around including create/delete APIs for MBeans. 
>>>> In lieu of the above, as of now REST adapter cannot exist independently and will have to live along-side RMIConnector. 
>>>> -Harsha
>>>> 
>>>> On Monday 11 September 2017 09:05 PM, Kirk Pepperdine wrote:
>>>>> Hi Harsha,
>>>>> 
>>>>> The only reason I mentioned Jolokia is that it’s a project that usefulness is some what limited because it is *not* a compliment JMX connector and as such cannot be used as a straight drop-in replacement for the current RMI based connector. Is your plan here to make it a fully compliant connector so that we could configure tooling such as the MBean viewers in jConsole and VisualVM (or JMC for that matter) to use a restful connector instead of an RMI based connector? IMHO, doing so would represent a huge win as I know of quite a few projects that cannot or will not use JMX because of it’s reliance on RMI.
>>>>> 
>>>>> Consolidating all of the options under a single flag looks like another interesting win.
>>>>> 
>>>>> Kind regards,
>>>>> Kirk
>>>>> 
>>>>> 
>>>>> 
>>>>>> On Sep 11, 2017, at 4:08 PM, Harsha Wardhana B < <mailto:harsha.wardhana.b at oracle.com>harsha.wardhana.b at oracle.com <mailto:harsha.wardhana.b at oracle.com>> wrote:
>>>>>> 
>>>>>> Hi Erik,
>>>>>> 
>>>>>> On Monday 11 September 2017 07:14 PM, Erik Gahlin wrote:
>>>>>>> Hi Harsha,
>>>>>>> 
>>>>>>> I haven't looked at Jolokia, or know what is the most reasonable approach in this case, but as a principle, I think we should strive for the best possible design rather than trying to be compatible with third party tools.
>>>>>> Agreed. That will always be the first priority. That is the reason HTTP GET interfaces will not be changed. I am undecided if the POST payloads need to be changed (without compromising the REST design principles) to increase adoption of this feature. 
>>>>>>> 
>>>>>>> How will the command line look like to start the agent with the rest adapter?
>>>>>>> 
>>>>>>> In the past there have been discussions about adding syntactic sugar for -Dcom.sun.management, i.e.
>>>>>>> 
>>>>>>> -Xmanagement:ssl=false,port=7091,authenticate=false
>>>>>>> 
>>>>>>> instead of
>>>>>>> 
>>>>>>> -Dcom.sun.management.jmxremote.ssl=false 
>>>>>>> -Dcom.sun.management.jmxremote.port=7091
>>>>>>> -Dcom.sun.management.jmxremote.authenticate=false 
>>>>>>> 
>>>>>>> which is hard to remember, cumbersome to write and error prone since the parameters are not validated. If we are adding support for REST, it could perhaps be default, i.e.
>>>>>>> 
>>>>>>> -Xmanagement:ssl=false,authenticate=false,port=80
>>>>>>> 
>>>>>>> If you want to use JMX over RMI you would specify protocol:
>>>>>>> 
>>>>>>> -Xmanagement:ssl=false,port=7091,authenticate=false,protocol=rmi
>>>>>> Yes. There is an enhancement request to add the -Xmanagemet:* syntatic sugar for -Dcom.sun.management.jmxremote.* flags. REST adapter will use one of the above flags though I haven't thought of the exact name for it yet. I will update the JEP with the details of the flag shortly. 
>>>>>>> 
>>>>>>> Has there been any thoughts about JMX notifications?
>>>>>> Notifications will not be supported in this JEP. 
>>>>>> MBean Notifications are not a widely used feature and will not be supported via the REST adapter.
>>>>>>> 
>>>>>>> I know it is outside the scope of the JEP, but I think we should take it into consideration when doing the design, so the functionality could be added on later without too much difficulty.
>>>>>> Notifications can be added without modifying the current design too much. If required, it will be worked upon via an enhancement request. 
>>>>>>> 
>>>>>>> Thanks
>>>>>>> Erik
>>>>>>> 
>>>>>> Thanks
>>>>>> Harsha
>>>>>>>> Hi Martin,
>>>>>>>> 
>>>>>>>> In my opinion, the interfaces exposed by current JEP are lot closer to REST style than the interfaces exposed by Jolokia. 
>>>>>>>> For instance, HTTP GET by default should be used to read resources, but it is made part of URL in Jolokia interfaces.
>>>>>>>> 
>>>>>>>> <base-url>/read/<mbean name>/<attribute name>/<inner path>
>>>>>>>> 
>>>>>>>> I would wait on opinions from more people before considering changing the current interfaces.
>>>>>>>> 
>>>>>>>> Thanks
>>>>>>>> -Harsha
>>>>>>>> 
>>>>>>>> On Wednesday 06 September 2017 11:40 AM, Martin Skarsaune wrote:
>>>>>>>>> Hello
>>>>>>>>> 
>>>>>>>>> Would one at least consider adopting the same URL paths and payloads as Jolokia? This could make life a lot easier for third party tools that connect to it. 
>>>>>>>>> 
>>>>>>>>> Best Regards
>>>>>>>>> 
>>>>>>>>> Martin Skarsaune 
>>>>>>>>> 
>>>>>>>>> ons. 6. sep. 2017 kl. 07:04 skrev Harsha Wardhana B < <mailto:harsha.wardhana.b at oracle.com>harsha.wardhana.b at oracle.com <mailto:harsha.wardhana.b at oracle.com>>:
>>>>>>>>> Hi Kirk,
>>>>>>>>> 
>>>>>>>>> Yes. Jolokia was considered and is listed as an alternative in the JEP.
>>>>>>>>> 
>>>>>>>>> Jolokia can serve as a viable alternative but can be bulky. We are looking for simple and lightweight solution.
>>>>>>>>> 
>>>>>>>>> -Harsha
>>>>>>>>> 
>>>>>>>>> On Wednesday 06 September 2017 10:21 AM, Kirk Pepperdine wrote:
>>>>>>>>>> Hi,
>>>>>>>>>> 
>>>>>>>>>> Have you run into this project? https://jolokia.org <https://jolokia.org/>. Unfortunately it’s not exactly a drop in replacement for the standard RMI based JMX connector but it’s not far off.
>>>>>>>>>> 
>>>>>>>>>> Kind regards,
>>>>>>>>>> Kirk
>>>>>>>>>> 
>>>>>>>>> 
>>>>>>>>>>> On Sep 5, 2017, at 6:30 PM, Erik Gahlin <erik.gahlin at oracle.com> <mailto:erik.gahlin at oracle.com> wrote:
>>>>>>>>>>> 
>>>>>>>>>>> Hi Harsha,
>>>>>>>>>>> 
>>>>>>>>>>> Looping in jmx-dev.
>>>>>>>>>>> 
>>>>>>>>>>>> byte[], short[], int[], float[], double[]
>>>>>>>>>>> Should long[] be included there as well?
>>>>>>>>>>> 
>>>>>>>>>>>> The REST adapter will come with a simple and lightweight JSON parser.
>>>>>>>>>>> Is this an internal parser or will it be exposed as an API?
>>>>>>>>>>> 
>>>>>>>>>>> If so, how does it relate to JEP 198: Light-Weight JSON API?
>>>>>>>>>>> http://openjdk.java.net/jeps/198 <http://openjdk.java.net/jeps/198>
>>>>>>>>>>> 
>>>>>>>>>>> Will com.sun.net.httpserver.HttpServer be used to serve the requests?
>>>>>>>>>>> 
>>>>>>>>>>> Thanks
>>>>>>>>>>> Erik
>>>>>>>>>>> 
>>>>>>>>>>>> Hi All,
>>>>>>>>>>>> 
>>>>>>>>>>>> Please review the JEP for REST APIs for JMX :
>>>>>>>>>>>>        https://bugs.openjdk.java.net/browse/JDK-8171311 <https://bugs.openjdk.java.net/browse/JDK-8171311>
>>>>>>>>>>>> 
>>>>>>>>>>>> The JEP aims at providing RESTful web interfaces to MBeans.
>>>>>>>>>>>> 
>>>>>>>>>>>> Access to MBeans registered in a MBeanServer running inside a JVM requires a Java client. Language-agnostic access to MBeans will require spawning a Java client which can be cumbersome. The proposed JEP allows MBeans to be accessed in a language/platform-independent, ubiquitous and seamless manner.
>>>>>>>>>>>> 
>>>>>>>>>>>> Thanks
>>>>>>>>>>>> -Harsha
>>>>>>>>>>>> 
>>>>>>>>>>>> 
>>>>>>>> 
>>>>>>> 
>>>>>> 
>>>>> 
>>>> 
>>> 
>> 
> 

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