<p>Your load balancer usually offers this as configuration. Using HAProxy as an example (this is similar for most load balancers) you can change:</p>
<ol>
<li>Whether a server is in balance or not</li>
<li>What proportion of traffic it should receive</li>
<li>What strategy to use to divide traffic between servers</li>
</ol>
<p>Common use cases for this would be:</p>
<ul>
<li>Taking a server out of balance (and allowing existing connections to drain) before running a deployment, then warming it back up with a slower rate of traffic.</li>
<li>Splitting a small proportion of traffic for a canary release, which you might also use &quot;session pinning&quot; for, to make sure a canary user <em>stays</em> on the canary server, rather than flip-flopping between the old and new version</li>
</ul>
<p>With HAProxy, you can perform some operations via the command line to take servers in and out of balance. For the load balancing strategy, you'd normally change the config and reload it (which, again, you could automate via the command line).</p>
<p>It's not uncommon for people to set up HAProxy with &quot;redispatch&quot; configured. They can then surprise it by deploying to a server without telling it. HAProxy will receive the failure and re-send the request to a different server. The user has no idea there was any issue. You need to make sure this doesn't cause a domino effect in your scenario.</p>
<p>Nginx is pretty similar. Other load balancers offer things like REST APIs for these operations.</p>

CC BY-SA 4.0
2023-03-24T09:59:53.920Z
Appreciate the clarification !!
Chel MS
CC BY-SA 4.0
2023-03-22T11:36:54.087Z
2023-03-22T11:36:54.087Z
Fenton
<p>How does a <code>L4</code> or <code>L7</code> load balancer knows how to route traffic during deployments.
Say, In <code>Canary</code> deployment strategy, how does LB route only 10% traffic to a certain server or in case of <code>Blue-Green</code> deployment strategy, how does LB knows that the updated application is available on another set of servers and I should be routing the traffic to them.</p>
<p>Where should we make those configuration ideally ?</p>

<continuous-deployment><nginx><load-balance><high-availability>
Load balancing while deployment
Chel MS
# Load balancing while deployment

(Asked by: username_0 on 2022-07-25)

How does a `L4` or `L7` load balancer knows how to route traffic during deployments.
Say, In `Canary` deployment strategy, how does LB route only 10% traffic to a certain server or in case of `Blue-Green` deployment strategy, how does LB knows that the updated application is available on another set of servers and I should be routing the traffic to them.

Where should we make those configuration ideally ?

**Tags:** continuous-deployment, nginx, load-balance, high-availability


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## 1 answers

### Answer by username_1 on 2023-03-22. Score: 1 | Accepted answer

Your load balancer usually offers this as configuration. Using HAProxy as an example (this is similar for most load balancers) you can change:

1. Whether a server is in balance or not
2. What proportion of traffic it should receive
3. What strategy to use to divide traffic between servers

Common use cases for this would be:

* Taking a server out of balance (and allowing existing connections to drain) before running a deployment, then warming it back up with a slower rate of traffic.
* Splitting a small proportion of traffic for a canary release, which you might also use "session pinning" for, to make sure a canary user *stays* on the canary server, rather than flip-flopping between the old and new version

With HAProxy, you can perform some operations via the command line to take servers in and out of balance. For the load balancing strategy, you'd normally change the config and reload it (which, again, you could automate via the command line).

It's not uncommon for people to set up HAProxy with "redispatch" configured. They can then surprise it by deploying to a server without telling it. HAProxy will receive the failure and re-send the request to a different server. The user has no idea there was any issue. You need to make sure this doesn't cause a domino effect in your scenario.

Nginx is pretty similar. Other load balancers offer things like REST APIs for these operations.

> **Comments:**
> **username_0**: Appreciate the clarification !!  

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