DougBreaux 270007SMYJ Visits (4777)
If you've ever wanted to know what kind of HTTP Request headers might be coming from a client or some intermediate proxy, here's a simple JSP you can manually deploy to your JEE Web Application to see a list.
DougBreaux 270007SMYJ Visits (5177)
An oldie, but still useful from time to time.
Ever wonder which Jar or directory contains a class you're using in your JEE Web Application? Or which of multiple provider Jar files is the one being used? Or even whether or not a particular class is found at all?
No need to actually include it in your Web App permanently, but easy to deploy manually if you ever need it.
During investigation of some intermittent problems in one of our web applications, we observed some JSESSIONID cookie behavior that we couldn't explain, so I performed some investigation into the cookie's mechanics. I'll attempt to summarize in this article what I learned.
JSESSIONID Cookie Format
In a clustered environment, the JSESSIONID cookie is composed of the core Session ID and a few other components. Here's an example:
It's still unclear to me what the different values mean here, but searching our Proxy logs indicates that the vast majority of our Sessions, the Cache ID is 0001. For instance, a search of one day's log around 17:00 indicates the following number of cookies which contained a particular Cache ID:
For a particular Session ID, the Cache ID can definitely change mid-session, without any other changes. In particular, without the Clone/Partition ID changing. This does not indicate a switch to another Cluster member, but I don't know exactly what it does indicate. Based on the relative loads of our various systems, it seems possible that changing Cache IDs only occurs under heavy loads.
A Partition ID is appended to the cookie if memory-to-memory replication in peer-to-peer mode is utilized for Distributed Session management. Otherwise, a Clone ID is appended.
This will match one of the CloneID attributes in the Server elements within the web server's plugin-cfg.xml file. For instance 138888kcd in:
<Server CloneID="138888kcd" ConnectTimeout="10" Exte
If you use memory-to-memory Session replication, your cookies will contain Partition IDs rather than Clone IDs.
Partition IDs are similar in function to Clone IDs, but best I can tell there is no direct way to determine which values correspond to which cluster members. They are internally mapped by the WebSphere HAManager to specific Clone IDs, and that mapping is exchanged with the web server plug-in so that it can maintain Session affinity and find additional cluster members for failover. (The exchange takes place in private headers on each response from WAS back to the plug-in, and those headers are removed before the response is sent back to the client.)
Session Affinity and Failover
The Clone/Partition ID corresponds to whichever cluster member creates the Session, and the plug-in is responsible to send that Session to the same cluster member as long as it is available. From the Scalability Redbook:
Since the Servlet 2.3 specification, as implemented by WebSphere Application Server V5.0 and higher, only a single cluster member may control/access a given Session at a time. After a Session has been created, all following requests need to go to the same application server that created the Session. This Session affinity is provided by the plug-in.
If on a subsequent request the specified cluster member is unavailable, the plug-in will choose another cluster member and attempt to connect to that. If Distributed Sessions are configured, via database persistence or memory-to-memory replication, the Session will be resumed in-progress on that new member. If not, a new Session will be created and the user's progress will be lost.
If a new cluster member is able to resume the existing Session, it will append its own Clone/Partition ID to the existing JSESSIONID cookie. For instance:
Now the plug-in knows that 2 different cluster members could potentially service this Session. If the original member becomes available again, the Session will switch back to it.
Finally, note that according to the System Management Redbook:
WebSphere provides session affinity on a best-effort basis. There are narrow windows where session affinity fails. These windows are:
Referenced articles and Redbooks
DougBreaux 270007SMYJ Visits (5636)
Here is the URL for this bookmark: http
Server version: IBM_
DougBreaux 270007SMYJ Visits (8852)
After attending a webcast on the WebSphere Application Server 6.1 Plug-in, I thought I'd summarize the content I found helpful.
The plugin is a native module (DLL or .so) that is installed into the Web Server and is offered each HTTP request to determine whether WAS should handle it. It makes this determination based on the contents of the plugin-cfg.xml file which is normally auto-generated by WAS.
I say, "normally", because it can be manually edited, but doesn't need to be for most operating scenarios. Note that many of these customizations can now be configured within the Administrative Console as well, which significantly reduces the need for manual file editing. This configuration is located under Servers -> Web Servers -> <Server Instance> -> Plug-in Properties. (Visiting this location in the Console is also a useful way to to locate the active plugin configuration file.)
The configuration file specifies virtual hosts (IP names/addresses and ports) and URL paths which are serviced by WAS applications, enabling the plugin to determine which requests it can route to WAS and which it must leave for the HTTP server to handle.
The file also contains values governing performance, maintenance, and failover, such as logging configuration and network timeouts.
Finally, it contains the "transport" information used to forward matched requests to the appropriate Web Containers in WAS. That is, the IP name and port combinations of the different Cluster members' Web Container "Transport Chains".
"Affinity" is the notion of sending a user to the same Cluster member (application server JVM) for each subsequent request after the initial one, if the application uses HTTP Sessions. This behavior is required by the JEE specification, and in WebSphere is the responsibility of the Web Server plugin. WebSphere maintains this affinity by appending a "Clone ID" or "Partition ID" to the "Session ID", which the plugin then compares against its configuration to correctly route subsequent requests.
For further detail on the Session ID mechanics, see this post.
New users, those without an existing Session, are distributed to Cluster members in either a weighted round-robin fashion or a random fashion. Round-robin is the default, and it will decrement each cluster member's "weight" each time it sends it a new request, until all members are less than zero, then they will all be reset to their starting values.
Tips or Items of Note
Have you ever discovered that you no longer have the EAR file for the specific version of an Enterprise Application which is deployed on one of your systems?
It turns out WebSphere keeps a copy around that can be retrieved and re-deployed elsewhere. For the Network Deployment edition of WAS v6.1, you can find a deployed EAR file in:
(Note the ear name twice, first as a directory, then as a file.)
DougBreaux 270007SMYJ Visits (14790)
Each user on the system will have its own keystore where its public and private keys are stored. This keystore can be protected by a separate password or can be synchronized such that it's protected by the normal login password. I believe this is a system-wide setting, and the default is to synchronize the passwords. User keystores are located in /var
If a user is explicitly granted access to act as a specific group in relation to EFS (in addition to being assigned to that group at the OS level), the group's private and public keys will also be copied into the user's keystore.
Groups also have their own keystores, located in /var
Each file is encrypted with a unique, symmetric (AES) key. For each user or group that is authorized to view the encrypted file, the symmetric key is then itself encrypted with the user/group's public key from its keystore, and that user-specific encrypted version of the key is stored in the file's extended attributes (EAs). That is, there will be one EA for each user and group that has access to the file in question. (See section 2.4 of the AIX V6 Advanced Security Redbook.)
Requirements & Constraints
Tips & Specific Commands
Note: based on this article which I've only recently seen and haven't yet fully parsed, those last two items may no longer be true starting with AIX 6.1 TL4.
DougBreaux 270007SMYJ Visits (3966)
gunzip -c file.gz | tar xvf -
Edit: As a colleague pointed out, some flavors of UNIX have the -z flag in tar. This is for those which don't (like AIX).
If you just stop an application to make it unavailable, it will still be automatically started whenever the server where it resides is restarted. To disable an application entirely, but leave it installed, you can change the "autostart" settings under the application's "Target specific application status" (WebSphere 6.1).
Web Application Configuration
This is the basic annotation-based JAX-RS coding. See the below "Getting Started" article, Part 1 of the "RESTful Web services" article, and the Developing JAX-RS Web applications section of the WebSphere Feature Pack documentation.
It's a straightforward, portable way to define the URI Paths of your Resources, the HTTP Methods supported by them, the Parameters passed to them, the Content Types supplied by them, and more.
DougBreaux 270007SMYJ Visits (3502)
Do you use Delicious or the Book
I bookmark everything I think I might want to find again, even on subjects I don't currently need but might need in the future. A quick, easy search capability makes this a powerful tool. To that end, I use Firefox bookmark Keywords to search tags within bookmarks, all from the URL bar.
Then I can type, say,
To find everything I've tagged with both "websphere" and "jax-rs". Or
To find everything everyone on DeveloperWorks has similarly tagged. Here are some search strings to use with both DeveloperWorks' Bookmarks and Delicious:
Bonus Tip: in many modern browsers, including Firefox, Alt-Enter will open a new tab to display the results of the submitted request. Use that here to bring up your search results in a new tab.
This post is intended to document procedures which can be used to simplify and increase security of remote login procedures to UNIX systems through use of SSH private and public keys.
PuTTY for Windows
Creating an SSH private key
PuTTYgen is used for this step. Use the "Generate" button and follow the instructions.
You can choose RSA or DSA key types, and you can change the key size.
Enter a passphrase and "Save private key" somewhere on your local system. Note: Use a passphrase that you can remember but that is stronger than a normal password. Security people usually suggest using whole sentences or combinations of words/phrases. Later we'll configure another program so that you don't have to type this passphrase very often.
Installing the public key on the remote system
There are various ways to do this, but the PuTTYgen window explains what I've found to be the easiest. That is, copy the text from the Key text area at the top of the window and manually add it to the $HOM
The authorized_keys file probably doesn't yet exist, and the .ssh directory may or may not. (The same directory is where ssh places the known_hosts file that contains the public keys for hosts which you have trusted for ssh connections in the past.)
If either doesn't exist and has to be created, ensure that the permissions are as follows
Each line in authorized_keys can also be configured with further options, including restricting a key's use to specific hosts, for instance. The best documentation I found on those options is at this Free BSD man page.
You can, and probably will want to, install the exact same public key on each system on which you want to use key-based authentication.
Using the key pair to login with puTTY
This is the "manual" approach, which isn't necessary if you follow the next step, but I wanted to document it for completeness. Here we explicitly tell a PuTTY session that we'll be authenticating with the private key file we saved earlier.
If you use this approach, when you connect to the remote system, you'll be prompted to enter your private key's passphrase:
You could argue that's actually worse usability than the user ID/password solution since you'll be typing a much longer passphrase, which is where the next step comes in handy.
Automatic key usage with Pageant
Another of the PuTTY programs, Pageant, can act as an agent providing access to private keys and only requiring you to authenticate once for each key.
Once you've added this key file to Pageant and entered your passphrase there, you can leave Pageant running, and all the PuTTY programs will be able to authenticate with your key without your further involvement. In fact, with Pageant running, any attempts to connect to a host which trusts your key will automatically connect even if you haven't explicitly configured your PuTTY session to use key authentication. (See the default, enabled "Attempt authentication using Pageant" checkbox in the above PuTTY screenshot.)
Furthermore, the Pageant tray icon can actually be used to directly launch any saved PuTTY sessions you've created. Right-click on the tray icon and select "Saved Sessions".
Finally, you can use the command-line to pass to Pageant any private keys you want it to automatically load when it starts. This allows you to create a shortcut icon that will prompt you for the necessary passphrases and then start a copy of Pageant ready to be used for subsequent, key-authenticated SSH sessions:
Following up on Part 1, here's an additional tip which I use frequently. That is, when I need to tunnel SSH through one machine to reach others, using a background proxy with SSH key authentication for the initial connection simplifies this 2-hop process.
Automatic proxying with Plink
The PuTTY installation also includes a command-line SSH program called Plink which can be used in a "background" mode. The PuTTY help describes how to use Plink as a local proxy program, creating a background tunnel for the main PuTTY window. This configuration is performed in the Window > Proxy tab:
Specify a Proxy type of local, and the standard SSH Port, 22.
In the Proxy hostname field, you enter a host to which you have direct access and on which you've configured key authentication, then you refer to that host via the %proxyhost variable in the plink command you provide as the local proxy:
\path\to\plink -l %user %proxyhost -nc %host:%port
The %host and %port variables represent the ultimate destination Host Name and Port fields from the main PuTTY Session tab (which, as usual, you can enter as needed or save under separate Sessions for each server).
%user and %proxyhost are from this configuration page.
Note: If your Default Settings PuTTY profile has a username (on the Connection > Data tab) or hostname configured in it, plink will use those automatically. Discovering that wasted a couple of hours for myself and a colleague. On the other hand, if the configured default username matches your username on the proxy server, you can completely omit the -l parameter from the plink command.
Tunneling additional Ports
Furthermore, this technique can be used in conjunction with "normal" SSH tunneling (Connection > SSH > Tunnels) in order to tunnel a localhost port through both hops. For instance, to tunnel the default WebSphere Application Server administration console port:
Then you connect your browser to http
You can similarly 2-hop tunnel X-Windows by enabling X11 Forwarding on PuTTY's Connection > SSH > X11 tab. (You'll need Windows X server like XMing.)
Any additional tips you've found useful? Better ways to accomplish these same tasks? I welcome your comments and suggestions.
I sometimes need to set a custom JVM Property for one or more Application Servers and dislike the tedium of setting them one-at-a-time through the console.
Here's a Jyth
wsadmin -f addJvmProperty.