On Nov 7, 2008, at 1:58 PM, Julio Faerman wrote:
> I would like to discuss this further, i think it is a very common
> question. Let me try do defend some "statefulness".
>
> 1- The overhead of session management is questionable, as there are
> efficient persistence and replication mechanisms available in modern
> app servers. If we are talking about a sufficiently large number of
> server, the overhead is tolerable.
>
It is yet another thing to manage and consider, especially when the
deployment system changes. It makes it harder to route requests to the
right set of machines each time. The implications of such session
state can cross many boundaries in the layered and networked system,
including clients, for example i cannot switch from buying an airline
ticket on my laptop, bookmarking the URL, and switching to continue
the process on my phone, perhaps in another country deferring to a
bunch of servers close to my location for better performance.
> 2- The use of HTTP-Basic auth is less secure, specially if not using
> SSL.
>
As the name suggests it is basic :-) but i would argue no less basic
than many Web apps that send the password typed into the HTML form as
part of the POST login message. Both have to be used with SSL.
> 3- The session helps a lot when the information the system should
> provide is contextualized to the authenticated user. For example,
> showing the accounts of the salesperson using the system. A stateless
> app would require additional authorization checks to perform the same
> operation.
When you log in you have to authenticate and that authentication
grants roles. Is that not independent of the authentication mechanism?
The key i think is to ensure that the contextualized information is
resource state identified by a URI associated with the user, or
application state that is sent by the client to the server.
>
>
> I tried hard to keep my current project completly "stateless", and i
> agree on storing the minimum possible state in the session, but the
> benefits of a small session outweights the cost in most applications,
> IMHO.
>
I understand, pragmatically i can see why this is so. As i said i
think the tools/frameworks have made it easy to leverage sessions
rather than other mechanisms that do not leverage sessions that make
better use of URIs.
Paul.
> On Fri, Nov 7, 2008 at 6:25 AM, Paul Sandoz <Paul.Sandoz_at_sun.com>
> wrote:
>> Hi Craig,
>>
>> Well said! Further more you often find that some web sites will be
>> hidden
>> behind one URL. It is not book markable.
>>
>> The current state of affairs is this: at any one point in time how
>> to do you
>> know web sites you are logged into? how do you log out? the browser
>> does not
>> know really anything, because it is all opaque through server-given
>> opaque
>> identifiers, usually cookies.
>>
>> Would it not be nice for the browser, and therefore the user, to
>> have more
>> control over this? Utilizing HTTP authentication can enable this
>> because the
>> browser is aware of the authentication process. Unfortunately
>> browsers today
>> do a dreadful job popping up an ugly dialog box to login. I am sure
>> there
>> are ways to get nice login pages working with this type of
>> mechanism but the
>> frameworks and tools do not encourage this type of approach, thus
>> the least
>> path of resistance is to use a session, which can easily come to be a
>> decision one might regret later on.
>>
>> Paul.
>>
>> On Nov 7, 2008, at 9:11 AM, Craig McClanahan wrote:
>>
>>> Craig McClanahan wrote:
>>>>
>>>> Eduardo Pérez Ureta wrote:
>>>>>
>>>>> Ideally I would like to use the servlet session.
>>>
>>> I should have responded to this particular statement in my previous
>>> response (sorry for the omission). And it relates to some
>>> comments I *did*
>>> make that might not make a lot of sense without a little bit of
>>> context.
>>>
>>> One of the key principles behind RESTful APIs is that they should be
>>> *stateless*. In other words, if the server is implemented as
>>> multiple
>>> instances of your application behind a load balancer, it should
>>> not matter
>>> if the (n)th request and the (n+1)th request are served by different
>>> instances. This is a key attribute in designing an application
>>> that can
>>> scale beyond a single server instance.
>>>
>>> When you use servlet sessions, you are risking a violation of this
>>> basic
>>> principle. Let's assume that you are taking the typical approach
>>> where a
>>> cookie is used to tell the client what session identifier to
>>> submit on
>>> subsequent requests. The usual server side implementation of a
>>> "session" is
>>> essentially a HashMap of session attributes, keyed by the session
>>> id. But
>>> the *crucial* point is that this information normally lives only
>>> within the
>>> context of a single JVM (i.e. a single instance of your server).
>>> Supporting
>>> an application that scales horizontally (that is, across multiple
>>> server
>>> instances) would require that either:
>>>
>>> * the load balancer recognize that a subsequent request belongs to
>>> an
>>> existing session on a *single* instance of your application, which
>>> means
>>> you are likely to experience service overloads if this single
>>> instance has
>>> too many active sessions. (You will often see this referred to as
>>> "sticky
>>> sessions").
>>>
>>> * the server environment recognizes that there is an existing
>>> session, but
>>> the data for it lives on some other server instance so it needs to
>>> be
>>> copied
>>> to this instance before the request can be processed. As you can
>>> imagine,
>>> there can be significant overhead in doing this sort of thing.
>>>
>>> With respect to authentication (which was the particular context of
>>> Eduardo's questions), the standard HTTP approach is to include an
>>> HTTP
>>> header named "Authorization" with each request -- most typically
>>> using the
>>> HTTP Basic authentication scheme (http://www.ietf.org/rfc/rfc2617.txt
>>> ).
>>> This means that the authentication operation must occur on *every*
>>> request,
>>> but it also means that you can indeed scale your application
>>> across multiple
>>> server instances, because any one of them is capable of performing
>>> the
>>> authentication transaction. You would be wise, if you are
>>> planning on an
>>> application that does, or even *might*, require deployment of more
>>> than one
>>> instance, to keep this consideration in mind.
>>>
>>> For a Java developer who doesn't want to care about all the
>>> nuances and
>>> complexities of the HTTP protocol, my recommendation is pretty
>>> simple --
>>> figure out how to design your application without using sessions.
>>> For
>>> authentication, that's pretty simple ... just include the
>>> authorization
>>> header on each request (for human-interaction web applications,
>>> browsers
>>> even do this for you if your server is designed for HTTP Basic
>>> authentication). For application state, everything that the
>>> server needs to
>>> know about the current state should be included with each
>>> request. (The
>>> details of this topic is the source of many thesis-length
>>> dissertations, but
>>> the fundamental principle is pretty easy to grok.)
>>>
>>> Or, of course, if you *know* your application will never need more
>>> than
>>> one instance (even to ensure availability in the case of an instance
>>> failure), you can safely ignore this advice. But can you really
>>> be sure?
>>> (For a 10-user departmental app behind your company firewall, sure
>>> you can.
>>> For an Internet facing app, no way IMHO. All it takes is a single
>>> "Slashdot Effect" surge of interest in your app, which overloads
>>> your single
>>> server instance, to demonstrate to you (and to the world,
>>> unfortunately)
>>> that you weren't ready for Internet scale user traffic).
>>>
>>> Craig
>>>
>>>
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