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  • Managing hosts and iptables in scalable architecture

    - by hakunin
    Let's say I have a load balancer in front of 3 app servers. Let's say I also have these services available at certain IPs: Postgres server Redis server ElasticSearch server Memcached server 1 Memcached server 2 Memcached server 3 So that's 6 nodes at 6 different IP addresses. Naturally, every one of my 3 app servers needs to talk to these 6 servers above. Then, to make it a bit funkier, I also have 3 worker servers. And each worker also talks to the above 6 servers, but thankfully workers and apps never need to talk to each other. Now's the kicker. Everything is on Digital Ocean VPS. What that means is: you have no private network, no private IPs. You only have separate, random IP address on each machine. You can't mask them or anything. So in order to build a secure environment I would have to configure some iptables. For example: Open app servers be accessed by load balancer server Open redis, ES, PG, and each memcached servers to be accessed by each app's IP and each worker's IP This means that every time I add an app or worker I have to also reconfigure iptables in those above 6 servers to welcome the new app or worker. Is there a way to simplify this type of setup? I was thinking — what if there was a gateway machine between apps/workers and the above 6 machines. This way all the interaction would always happen via the gateway server, and when I add a new app or worker I wouldn't need to teach the 6 servers to let it in. If I went this route, then I'd hope a small 512mb server could handle that perhaps, and there wouldn't be almost any overhead. Or would there? Please help with best way to handle this situation. I would appreciate an answer as concrete as possible. I don't think this is too specific, because this general architecture is very common, and Digital Ocean is becoming increasingly popular. A concrete solution here would be much appreciated by many.

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  • Two DHCP Servers, Block Clients for one of them?

    - by Rilindo
    I am building out a kickstart network that resides on a different VLAN uses its own DHCP server. For some reason, my kickstart clients kept getting assign IPs from my primary DHCP server. The way I have it set up is that I have a primary DHCP server on this router here: 192.168.15.1 Connected to that DHCP server is a switch with the IP of 192.168.15.2. My kickstart (Scientific Linux) server is connected to that switch on two ports: Port 2 - where the kickstart server communicates to the rest of the production network via eth0. The IP assigned to the server on that interface is 192.168.15.100 (on eth0). The details are: Interface: eth0 IP: 192.168.15.100 Netmask: 255.255.255.0 Gateway: 192.168.15.1 Port 7 - has it's own VLAN ID (along with port 8). The kickstart server is connected to that port with the IP of 172.16.15.100 (on eth1). Again, the details are: Interface: eth1 IP: 172.16.15.100 Netmask: 255.255.255.0 Gateway: none The kickstart server runs its own DHCP server and assigns them over the eth1. Most of the kick starts are built over the kickstart VLAN through port 8. To prevent the kickstart DHCP server from assigning addresses over the production network, I have the route setup like so: route add -host 255.255.255.255 dev eth1 At this point, the clients kept getting assign IPs from the 192.168.15.1 DHCP server. I need to figure out a way to block client requests from reaching that DHCP. Its should be noted that but I also build KVM hosts on the kickstart server as well, so I need those KVMs to have the ability to get DHCP requests from the 192.168.15.1 DHCP server via the bridge network once I finish resolved this particular problem. (Currently, they communicate via NAT). So what would be done to resolve this? Through iptables or some sort of routing I need to put in? I tried to limited to requests via IPtables on that interface, allowing DHCP requests for 172.16.15.x network: -A INPUT -i eth1 -s 172.16.15.0/24 -p udp -m udp --dport 69 -j ACCEPT -A INPUT -i eth1 -s 172.16.15.0/24 -p tcp -m tcp --dport 69 -j ACCEPT -A INPUT -i eth1 -s 172.16.15.0/24 -p udp -m udp --dport 68 -j ACCEPT -A INPUT -i eth1 -s 172.16.15.0/24 -p tcp -m tcp --dport 68 -j ACCEPT -A INPUT -i eth1 -s 172.16.15.0/24 -p udp -m udp --dport 67 -j ACCEPT -A INPUT -i eth1 -s 172.16.15.0/24 -p tcp -m tcp --dport 67 -j ACCEPT And rejects assignments on eth1 from 192.168.15.x network: -A FORWARD -o eth1 -s 192.168.15.0/24 -p udp -m udp --dport 69 -j REJECT -A FORWARD -o eth1 -s 192.168.15.0/24 -p tcp -m tcp --dport 69 -j REJECT -A FORWARD -o eth1 -s 192.168.15.0/24 -p udp -m udp --dport 68 -j REJECT -A FORWARD -o eth1 -s 192.168.15.0/24 -p tcp -m tcp --dport 68 -j REJECT -A FORWARD -o eth1 -s 192.168.15.0/24 -p udp -m udp --dport 67 -j REJECT -A FORWARD -o eth1 -s 192.168.15.0/24 -p tcp -m tcp --dport 67 -j REJECT Nope. :(

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  • Running OpenVZ virtual servers within a Xen XCP vritual server? Bad practice?

    - by Damainman
    I have a 1 server with 8GB RAM and 2xQuadcore Processors. It currently has the Xen XCP installed on it, and centos6.2 x64 running on a virtual machine. I have a server control panel software that I want to use and it allows the administration via a web interface for Openvz machines. My questions are: Would this be considered bad practice? Would there be a big performance hit? Should I avoid this all together or am I going about it all wrong? Thank you in advance.

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  • What is the best resource or method for learning more about servers and networking?

    - by kaleidomedallion
    I can get around a server to some degree, but everything I have learned has been as I have needed to learn it. Every once in a while I will learn about some new command that will revolutionize how I think about systems and networking, and realize how I could have been using it this whole time if only I had known about it. Anything to bring someone from novice to some kind of fluency? Do I just need to earn the battle scars bit by bit over the course of years? (I mean of course I do but what can I do to help it be not quite so painful?) For instance, I am still fuzzy on all of networking. Any help would be greatly appreciated.

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  • Is domain-transfer inherently safe for downtime when the name servers remain the same?

    - by jlmt
    I've been reading around this topic towards understanding whether there's some or no chance of downtime during an upcoming domain transfer for 15 live and very critical domains. In our case there are three companies involved: CompanyA is the original registrar and DNS host, CompanyB is the new DNS host, and CompanyC is the new registrar. I've already changed the nameservers for all domains to those of CompanyB. We suffered some downtime because CompanyA deleted their hosted DNS for our domains directly after the change, but the changes propagated and we're now able to configure our DNS with CompanyB. From what I understand (please correct where wrong!): There exists an SOA record that points oneofourdomains.com to ns.companyb.com. That record is maintained and authoritatively hosted by the ccTLD registry for the domain (eg. Verisign for .com). CompanyA currently has the ability to change the SOA record because they're the registrar. There exist NS records for oneofourdomains.com, which are also related to the link from domain name to nameserver, are similarly hosted by the ccTLD, and which CompanyA are also able to change while acting as registrar. Neither CompanyB nor CompanyC currently have any control over the SOA or NS records. CompanyA are unable to cause us (DNS) problems during the transfer by dropping service early, because they are not the authoritative source for the SOA and NS records. When we transfer the domains, it's administrative control of the SOA and NS records that will be transferred to CompanyC. As long as we advise CompanyC that the SOA and NS records must not change (as regards pointing to CompanyB's nameservers), there's no need for any kind of DNS change, and therefore no possibility of downtime. Is my understanding of this correct? My fear is that CompanyA will somehow cut us off again, and their support dept hasn't given me much confidence in their understanding of the topic.

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  • Logging Remote Desktop to Servers via Logon Script or GPO or What?

    - by Nate Bross
    The objective here is to start a simple .NET application I've written which captures some environment variables (time, username, computername, etc) upon login. This .NET application subscribes to the Windows "User logout" event. Upon launch, the application captures the above variables, and creates a record in my database, upon logout (which I'm capturing) I update another field in the same record, with the logout time. The above is working exactly as I would like, when I launch the binary, it makes its initial log entry, then waits for the logout event and updates the same record. Restrictions, the .NET binary should be able to live on a share point (\server\share\myapp\v1) so I can update the application to (\server\share\myapp\v2) and simply update the GPO/Logon script. My initial thought was to use the \domaincontroller\sysvol\ directory to store the binary and then update all user accounts to include a call to my application. Can you see any flaws in this approach? My question is this: First, is there anything wrong with my idea above? Second, if so, what is the best way (through group policy or otherwise) to ensure this application launches whenever a session is started on a server?

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  • Oracle: 1 Large Server vs. 2 Smaller Servers?

    - by nvahalik
    We are in the planning stages of setting up our production Oracle 10gR2 environment. Our budget gives us the ability to buy 2 processor licenses of Oracle DB Standard Edition. We have minimal experience with Oracle so I'll defer to anyone who has used it. We are trying to decide if we should set up a single dual quad-core box or 2 individual quad-core boxes in a RAC configuration. Our DB right now is about 60 GB, and at our peak, we'll have up to 150 concurrent users. Most of the big stuff is done via batch processing at night. My gut tells me that having 2 boxes in a RAC configuration can't be a bad thing because it provides a true hardware failover solution. DB stored in a shared LUN on a SAN via iSCSI. Plus if we ever need to add capacity, we already have boxes in place that can be upgraded with extra procs (I assume with zero downtime, since it's set up in a RAC config) if we add extra licenses, or RAM. Does RAC have any performance penalties? Will it add extra latency? Is there any true advantage for having dual processor boxes running these systems? If we build out the Oracle boxes with special hardware: hardware iSCSI cards, TOE NICs, will these boxes be solid? We are deploying on 64-bit Windows. So what would you do? One box or two?

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  • How do I capture and playback http web requests against multiple web servers?

    - by KevM
    My overall goal is to not interrupt a production system while capturing HTTP Posts to a web application so that I can reverse engineer the telemetry coming from a closed application. I have control over the transmitter of the HTTP Posts but not the receiving web application. It seems like I need a request "forking" proxy. Sort of a reverse proxy that pushes the request to 2 endpoints, a master and slave, only relaying the response from the master endpoint back to the requester. I am not a server geek so something like this may exist but I don't know the term of art for what I am looking for. Another possibility could be a simple logging proxy. Capture a log of the web requests. Rewrite the log to target my "slave" web application. Playback the log with curl or something. Thank you for your assistance.

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  • is it possible to have two web servers hosted at different places share the same domain name?

    - by patrick
    say I have a wordpress site: https://www.foobar.com and I want to have an entry point to a rails app at a certain subdirectory within that same domain: https://www.foobar.com/rails_app I know this is possible if both the wordpress app and the rails app are hosted on the same box, but is this in anyway possible if they are hosted on different boxes? I do not want to use subdomains because I am trying to allow ajax post requests from one to the other and not having to deal with single origin policy stuff.

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  • Is there any very bare minimal ftp server for ubuntu that wouldn't conflict with other installed servers?

    - by Disco
    I have installed proftpd with mod-sql modules; i need to have a ftp server that would run on another port (and use a separate authentication scheme) Whenever i try to install vsftpd or pureftpd it simply removes proftpd and dependencies; i'm guessing it's to prevent having conflicts ... Is there any 'very small' ftp server; like run from command line that I could use ? I've searched all around but cannot find ... Any help would be appreciated

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  • Migrate servers without losing any data / time-limited MySQL dump?

    - by inac
    Is there a way to migrate from an old dedicated server to a new one without losing any data in-between - and with no downtime? In the past, I've had to lose MySQL data between the time when the new server goes up (i.e., all files transferred, system up and ready), and when I take the old server down (data still transferred to old until new one takes over). There is also a short period where both are down for DNS, etc., to refresh. Is there a way for MySQL/root to easily transfer all data that was updated/inserted between a certain time frame?

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  • How to backup Servers to an SSH-Host with low traffic and access to versions and encryption?

    - by leto
    Hello, I've not run backups for the past dont't remember anymore years for my personal stuff until waking up lately and realising contrary to my prior belief: Actually. I care! :) Now I have a central data server at home where I want to attach an external media to, to which I want to save backups of my most important stuff, like years of self-written scripts, database dumps, you name it. I've tinkered with rsync+ssh over the last two years, also tried tar over ssh, but don't know the simplest and most easy to maintain way to do it yet. Heres my workload: A typical LAMP-Server (<5GB Data) which I'd like to backup fully so lots of small files connected via 10Mbit My personal stuff (<750GB Data) from a Mac connected via GE My passwords in an encrypted container (100Mb) from OpenBSD connected via serial-PPP My E-Mail from the last ten years (<25GB) as Maildir which I need to keep in readable format Some archives (tar.*) which I need to backup only once and keep in readable format (Deleted my ideas, as I'm here for suggestions) What I need: 1. Use an ssh-tunnel for data transfer 2. Be quick with lots of small files 3. Keep revisions 4. Be sure the data I save is not corrupted 5. Intelligent resume functions and be able to deal with network congestion :) 6. Compressed and optionally encrypted storage 7. Be able to extract data from backup easily (filesystem like usage would be nice) How would and with what software would you backup this stuff? Hints to tools that can help solve only part of my problem (like encryption) also greatly appreciated. Greets

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  • What other ways can I load balance EC2 servers without using Elastic Load Balancing?

    - by undefined
    I have a web application that consists of a web server managed by a web hosting firm, a set of EC2 instances in amazons cloud and a MySQL database (hosted on the webserver). MySQL is behind a firewall and is set to allow access from Localhost and from a single IP address which is an Amazon Elastic IP address that is attached to the EC2 instance I have been running up to now. The problem is that I want to look at my scaling up and load balancing strategy for my EC2 instance. To this end I have been investigating the Elastic Load Balancers and Autoscaling tools that Amazon provides and have managed to set this up fine but for one thing - connecting to the MySQL database running on my webserver. I realised (thanks to answers on Serverfault) that I needed to check firewall settings and add the IP address for the load balancer, however Elastic Load Balancers provide you with a DNS name, not an IP address and infact the IP addresses change over time so this will not work. I have been told by the company hosting the database that the way the firewall works is to look up the IP address of the DNS name and store the IP rather than the DNS name. so basically this will not work and the only way to allow access would be to open up the SQL port to allow access from anyone! Is this a viable idea? Should I look at moving my database into the cloud? Is there another firewall that the server company can use? Should I find another way of load balancing (if so what?) tricky one eh? any help appreciated!

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  • [openVPN] server & client on same machine . And multiple VPN servers

    - by HiWorld
    Hello everyone, im stucked configuring openvpn to build a multi vpn connection. like this: CLIENT - VPN1 - VPN2 - INTERNET Well, i already have and know how to done a normal sigle vpn but want to use a chain of vpns, so i explain what i have done and how i did it. ON VPN1. i have 1 openvpn instance running as server( where client connect to) and another as client connecting to VPN2 running as server. { Here comes the problem } when i connect VPN1 as client of VPN2 i cant connect to VPN1 from CLIENT, my question is HOW TO procced with this... Also have another third instance working as server to use VPN1 without chains. ON VPN2. 1 openvpn instance as server where VPN1 will connect and then forward to the NET. Im using TUN interface on configs. And iptables are on this way: VPN1 - openvpn ip server1 : 192.168.6.0 / ip as client of VPN2: 192.168.5.70 iptables -t nat -A POSTROUTING -s 192.168.6.0 -j SNAT --to-source 192.168.5.70 VPN2 - openvpn ip server2 : 192.168.5.0 iptables -t nat -A POSTROUTING -s 192.168.5.0/24 -j SNAT --to-source EXTERNAL_IP_TO_INTERNET Hope someone help me with this. thanks in advance

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  • How do shared hosting servers keep executing code from crossing accounts?

    - by acidzombie24
    I am kind of curious, how does a hosting server support multiple users with php but keep each user away from the other code? The 'easy' solution i thought were file permissions. So every user can have www-data belong to their group and the server would have executing access but the users cant access the others file. But then i realize the user running the php would be www-data who has permission to read everyones data. So how does a shared host prevent this from happening? PS: I personally use nginx (with fastcgi php). But i am somewhat familiar on how apache works.

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  • Which IMAP servers support both messages and subfolders in a folder?

    - by user43516
    Hi, I currently have a POP server for email, which is delivered to a Thunderbird client. This Thunderbird client stores email locally into a hierarchy of subfolders containing both emails and subfolders. I now want to access this locally stored email from other clients. My first solution was to create an IMAP mailbox and move all the messages to the IMAP server. I wasn't able to do it because my IMAP server refused to create subfolders in folders already containing email. As the original hierarchy is quite complex, I can't modify it to try to get along with this limitation. Are there any Linux IMAP server that would accept having both messages and subfolders in a folder?

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  • What is the best tool to aggregate traffic stats from multiple nginx servers?

    - by gekkz
    The setup: 2 or more nginx machines each machine has the same virtual hosts traffic is load balanced via DNS to each machine I need to figure out what are the best tools to use to get some traffic stats, mostly interested in amount of hits and total traffic in gigabytes. Obviously, the log information will come from nginx, formatted like this: log_format main '$remote_addr $host $remote_user [$time_local] "$request" ' '$status $body_bytes_sent "$http_referer" "$http_user_agent" "$gzip_ratio"';

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  • ASP.NET MVC 2 Hosting :: MVC2 deploy - Could not load file or assembly 'System.Web.MVC, Version=2.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35' or one of its dependencies.

    - by mbridge
    A new MVC 2 project worked on my local machine but when it was deployed to the test server it gave the error 'Could not load file or assembly 'System.Web.Mvc, Version=2.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35' or one of its dependencies.' I have the full Visual Studio 2010 installed on my local machine but just the .NET 4 framework installed on the test servers. It seems the MVC assemblies do not come with .NET 4 framework itself so how to make MVC 2 work on the test servers? When I installed Visual Studio 2010 on my local machine it came with all the fruit included (.NET4 framework, MVC2 etc) so the System.Web.Mvc.dll can be found in my machine's GAC (C:\Windows\assembly). However, since there is no need to bloat the web servers only the plain old .NET4 framework has been installed on the test servers. This does NOT include the MVC assembly and that is why it cannot be found by the web application. You need this assembly to be on your web servers that you are deploying to but you want to avoid having to copy them into the GAC manually and doing all that gacutil mess or maybe you don't have access to your servers if they are hosted by provider. Solution You need to make the System.Web.Mvc assembly bin deployable... okay that doesn't sound easy but here is how to do it for the necessary MVC references: Simply right click the reference and select 'Properties' Then change 'Copy Local' to 'True': Note If your server has .NET 3.5 sp1 installed the new(ish) assemblies System.Web.Routing and System.Web.Abstractions will already be in the GAC. If you had previously deployed an MVC 1 application to a .NET 3.5 server you may remember having to deploy the other two assemblies too. Since MVC2 requires at least .NET 3.5 sp1 you will not need to worry about these assemblies, just System.Web.Mvc

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  • We have multiple app servers running against a single database. How do I ensure that each row in a q

    - by Dave
    We have about 7 app servers running .NET windows services that ping a single sql server 2005 queue table and fetch a fixed amount of records to process at fixed intervals. The amount of records to process and the amount of time between fetches are both configurable and are initially set to 100 and 30 seconds initially. Currently, my queue table has an int status column which can be either "Ready, Processing, Complete, Error". The proc that fetches the records has a sql transaction with the following code inside the transaction: 1) Fetch x number of records into temp table where the status is "Ready". The select uses a holdlock hint 2) Update the status on those records in the Queue table to "Processing" The .NET services do some processing that may take seconds or even minutes per record. Another proc is called per record that simply updates the status to "Complete". The update proc has no transaction as I'm leaning on the implicit transaction as part of the update clause here. I don't know the traffic exceptions for this but figure it will be under 10k records per day. Is this the best way to handle this scenario? If so, are there any details that I've left out, such as a hint here or there? Thanks! Dave

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  • Why Illegal cookies are send by Browser and received by web servers (rfc 2109, 2965)?

    - by Artyom
    Hello, According to RFC 2109, 2965 cookie's value can be either HTTP token or quoted string, and token can't include non-ASCII characters. Cookie's RFC 2109 and RFC2965 HTTP's RFC 2068 token definition: http://tools.ietf.org/html/rfc2068#page-16 However I had found that Firefox browser (3.0.6) sends cookies with utf-8 string as-is and three web servers I tested (apache2, lighttpd, nginx) pass this string as-is to the application. For example, raw request from browser: $ nc -l -p 8080 GET /hello HTTP/1.1 Host: localhost:8080 User-Agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.0.9) Gecko/2009050519 Firefox/2.0.0.13 (Debian-3.0.6-1) Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8 Accept-Language: en-us,en;q=0.5 Accept-Encoding: gzip,deflate Accept-Charset: windows-1255,utf-8;q=0.7,*;q=0.7 Keep-Alive: 300 Connection: keep-alive Cookie: wikipp=1234; wikipp_username=?????? Cache-Control: max-age=0 And raw response of apache, nginx and lighttpd HTTP_COOKIE CGI variable: wikipp=1234; wikipp_username=?????? What do I miss? Can somebody explain me?

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  • How to get resultset with stored procedure calls over two linked servers?

    - by räph
    I have problems filling a temporary table with the resultset from a procedure call on a linked server, in which again a procedure on another server is called. I have a Stored Procedure sproc1 with the following code, which calls another procedure sproc2 on a linked server. SET @sqlCommand = 'INSERT INTO #tblTemp ( ModuleID, ParamID) ' + '( SELECT * FROM OPENQUERY(' + @targetServer + ', ' + '''SET FMTONLY OFF; EXEC ' + @targetDB + '.usr.sproc2 ' + @param + ''' ) )' exec ( @sqlCommand ) Now in the called sproc2 I again call a third procedure sproc3 on another linked server, which returns my resultset. SET @sqlCommand = 'EXEC ' + @targetServer +'.database.usr.sproc3 ' + @param exec ( @sqlCommand ) The whole thing doen't work, as I get an SQL error 7391 The operation could not be performed because OLE DB provider "%ls" for linked server "%ls" was unable to begin a distributed transaction. I already checked the hints at this microsoft article, but without success. But maybe, I can change the code in sproc1. Would there be some alternative to the temp table and the open query? Just calling stored procedures from server A to B to C and returning the resultset is working (I do this often in the application). But this special case with the temp table and openquery doesn't work! Or is it just not possible what I am trying to do? The microsft article states: Check the object you refer on the destination server. If it is a view or a stored procedure, or causes an execution of a trigger, check whether it implicitly references another server. If so, the third server is the source of the problem. Run the query directly on the third server. If you cannot run the query directly on the third server, the problem is not actually with the linked server query. Resolve the underlying problem first. Is this my case? PS: I can't avoid the architecture with the three servers.

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  • Why Illegal cookies are send by Browser and received by web servers (rfc2109)?

    - by Artyom
    Hello, According to RFC 2109 cookie's value can be either HTTP token or quoted string, and token can't include non-ASCII characters. Cookie's RFC 2109: http://tools.ietf.org/html/rfc2109#page-3 HTTP's RFC 2068 token definition: http://tools.ietf.org/html/rfc2068#page-16 However I had found that Firefox browser (3.0.6) sends cookies with utf-8 string as-is and three web servers I tested (apache2, lighttpd, nginx) pass this string as-is to the application. For example, raw request from browser: $ nc -l -p 8080 GET /hello HTTP/1.1 Host: localhost:8080 User-Agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.0.9) Gecko/2009050519 Firefox/2.0.0.13 (Debian-3.0.6-1) Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8 Accept-Language: en-us,en;q=0.5 Accept-Encoding: gzip,deflate Accept-Charset: windows-1255,utf-8;q=0.7,*;q=0.7 Keep-Alive: 300 Connection: keep-alive Cookie: wikipp=1234; wikipp_username=?????? Cache-Control: max-age=0 And raw response of apache, nginx and lighttpd HTTP_COOKIE CGI variable: wikipp=1234; wikipp_username=?????? What do I miss? Can somebody explain me?

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  • Are application servers necessary? Advantages of using one? (And other JEE questions)

    - by Mike
    Apologies for the long question.. there seems to be other similar questions on here but none really clear up my confusion. I'd be really grateful if someone could confirm or correct my understanding: Java Enterprise Edition is a set of APIs for building enterprise applications, which take away the burden of developing parts of the system that aren't actually features of the application you are trying to build (i.e. messaging, transactions etc). To do this, you can use an application server, which implements these APIs. So you could use JBoss, Glassfish, WebSphere, WebLogic etc which would provide your application with these enterprise services. However, there are many other implementations of these individual services available such as ActiveMQ for messaging, Hibernate for persistence, OpenEJB etc. You can download these implementations as Java libraries and include them in your application, and use the services they provide in a similar way to using the services provided by an application server. So if my understanding is correct, my questions are: I've read a lot of places that application servers are necessary for JEE features like EJB, but can't you just use an implementation such as OpenEJB and not need an application server at all? Are there any features that an application server provides which you cannot get from another source? Why would/wouldn't I choose an application server over a custom stack such as Tomcat, OpenEJB, ActiveMQ, and Hibernate? Is Spring a complete alternative to JEE? Does it ever require an application server or always just a servlet container? Why would someone choose Spring over JEE? Any help would be much appreciated!

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