SockJS and meteor: what if load balancer do not support sticky sessions? -

-

i'm exploring balancing options meteor. this article looks cool , says following should supported load balance meteor:

  1. mongo optailing. otherwise, may take ten seconds 1 instance of meteor updates another, because polling mongo driver used, polls-and-diffs db each ten seconds.
  2. websocket. it's clear - otherwise clients fallback http , long-polling, work, it's not cool websocket.
  3. sticky sessions 'which required sockjs'. here question comes:

as understood, 'sticky sessions support' assign 1 client same server during session. essential? may happen if don't configure sticky sessions @ all?

here's came myself:

  1. because meteor stores data sent client in memory, if client connects x servers, x times more memory consumed
  2. some minor (or major, if there no oplog) lag may appear same user in, say, different tabs or windows, may surprising.
  3. if sockjs reconnects , wants data persist across reconnections, gonna have bad time. i'm not sure how sockjs works, point valid?

what bad can happen? these 3 points doesn't bad: data valid, available, may @ cost of memory consumption.

basics

sticky sessions required ensure browser's in memory session can managed correctly server.

first let me explain why need sticky sessions:

each publish uses ordinary publish cursor keeps track of whatever collections client may have, when changes knows send down client. apply every meteor app if needs ddp connection. case websockets , sockjs

additionally there may other client session state stored in variables edge cases (e.g store user's state in variable).

the problem happens when server disconnects , reconnects, somehow perhaps connection gets transferred other node (without re-establishing new connection) - has no idea client's data, behaviour turn bit weird.

the issue sockjs & long polling

with sockjs there additional issue. sockjs uses websocket emulation when falls long polling.

with long polling new connection attempt/new http request made every time new data available.

if sticky sessions not enabled each of these connections randomly assigned different node/dynamo.

so have 50% chance (in case random) server has no idea client's ddp session every every time new data available.

it force client re-negotiate connection/ignore clients ddp commands , end getting weird behaviour on client.

half of these wrong node:

enter image description here


Comments

Post a Comment

Popular posts from this blog

php - Magento - Deleted Base url key -

-
i working on cleaning url: http://mydomain.com/shop/shop/deals i going through settings in configuration tab in admin panel on magento , change secure , unsecure base urls remove first base url "shop" web page read: http://mydomain.com/shop/deals so changed unsecure base urls mydomain.com/shop mydomain.com , secure 12.345.67.89/shop 12.345.67.89. wrong thing do. i cannot reload page or admin console. how access these files through ftp , change correctly there?? when make changes in admin panel changes made in database not in file. have make changes in database. 1.go database , select core_config_data table under table find web/unsecure/base_url , web/secure/base_url . make changes here. don't forget clear cache in var/cache folder
Read more

javascript - Tooltipster plugin not firing jquery function when button or any click even occur -

-
i want use tooltipster plugin click element in body show tooltip , want have close button inside tooltip close it. however use jquery click() function handle won't fired. tried solution in post. worked when tooltip triggered hover event. tooltipster plugin not firing jquery function when link in in tooltip clicked the original solution using hover in jsfiddle trigger: 'hover', instead using click show tooltip trigger: 'click', http://jsfiddle.net/bcqyl/7/ it won't fire click event in jquery block. can captured normal javascript function only. checked should code in tooltipster plugin locked , captured "click()" event inside tips when in click trigger mode. i tried other event onchange event of radio button fired when using code in original solution @evan right. tooltip doesn't exist in dom , can't bind/delegate action (even if go way $(document) after domready). if you're after close button inside of too...
Read more

java - WrongTypeOfReturnValue exception thrown when unit testing using mockito -

-
my test list<person> mylist; @test public void testisvalidperson() { mylist = new arraylist<person>(); mylist.add(new person("tom")); when(persondao.get(person)).thenreturn(mylist); when((persondao.get(person)).isempty()).thenreturn(false);//------exception thrown boolean result = service.isvalid("tom"); assertfalse(result); } method tested: public boolean isvalid(string person){ persondao = new persondao(); person personobj = new person(person); return (persondao.get(person).isempty())?false : true; } exception thrown: org.mockito.exceptions.misusing.wrongtypeofreturnvalue: boolean cannot returned get() get() should return list *** if you're unsure why you're getting above error read on. due nature of syntax above problem might occur because: 1. exception *might* occur in wrongly written multi-threaded tests. please refer mockito faq on limitations of concurrency testing. 2. sp...
Read more