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So, next Jelastic question!

I'm stuck using Spring Webflow for the time being, so sticky sessions in any load balanced scenario are important.

I'm trying to use the Jelastic Traffic Distributor to achieve Blue/Green deployments.

I have set up two servers and the TD infront of them. I've balanced the TD 100-0 in favour of server 1 and set the Routing Method to Sticky Sessions.

This setup appears to work great, all requests go to server 1 and the sessions are maintained there. Indeed the Sticky Sessions ensure if I move the balance to say 50-50, the sessions already created stick to server 1.

My hope was to achieve Blue-Green deployments by deploying new code into server 2 while the TD was still set to 100-0 balance in favour of server 1. Once the code was deployed I'd move the balance to 0-100 in favour of server 2. Old sessions would continue to run until they're finished with in server 1 (ie stick where they were stuck) while new sessions would be created and stuck to server 2 running the new code. Repeat in reverse for later deployments.

The documentation here implies this tactic should work, particularly the last line;

Also, upon setting 100% ratio for any server, the second one won’t be removed from the settings completely, so it will be able to process the already existing sessions

However what I'm seeing is that as soon as I move the balance to 0-100, the sessions previously stuck to server 1 are lost and all requests are balanced to server 2.

In other words the last line of the docs doesn't appear to be true?

Nick Foote
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1 Answers1

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There was incorrect information in our documentation:

Also, upon setting 100% ratio for any server, the second one won’t be removed from the settings completely, so it will be able to process the already existing sessions.

Our tech writers deleted this line from the documentation.

NGINX configuration with weight=0 isn't possible, NGINX will not be started with this parameter value, so it is expected behavior. When you set weight 0 in UI panel - backend server is excluded from NGINX configuration and all requests are directed to backend which remained in nginx upstreams.

There is another solution for you, you are able to set weight ratio 99:1 using UI (or e.g. 10000:1 using nginx-jelastic.conf in Traffic Distributor). In this case there is very small chance that session will be lost.

Virtuozzo
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