# Load balancer or service link?

**URL:** <https://forums.suse.com/t/load-balancer-or-service-link/4719>\
**Category:** Rancher 1.x\
**Created:** [November 26, 2016, 1:37pm UTC](https://forums.suse.com/t/load-balancer-or-service-link/4719 "2016-11-26T13:37:00Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![twoeo](https://avatars.discourse-cdn.com/v4/letter/t/c5a1d2/32.png) [@twoeo](https://forums.suse.com/u/twoeo)\
**Post date:** [November 26, 2016, 1:37pm UTC](https://forums.suse.com/t/load-balancer-or-service-link/4719/1 "2016-11-26T13:37:00Z")

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Both load balancer and service link can achieve high avaliability of service.  
Load balancer make it by a proxy, while service link by DNS.

Because this DNS is only belong to Rancher itself, public service can only use load balancer to distribute requests.

But to internal service, if service link is the same with load balancer ?  
Can service link be used for high avaliability ?

Whether the request may not be distributed balancedly because of DNS cache ?

For example:

Service `backend`, with 3 containers, `backend_1`, `backend_2`, `backend_3`

Service nginx, make a `proxy_pass` to `backend`.

**Would it always pass to `backend_1`, because once it DNS to `backend_1` and it will always use `backend_1` ?**

In other word, **can I use service link instead of load balancer for internal service ?**

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**Author:** ![vincent](https://sea2.discourse-cdn.com/flex022/user_avatar/forums.suse.com/vincent/32/7156_2.png) [@vincent](https://forums.suse.com/u/vincent)\
**Post date:** [November 28, 2016, 6:58am UTC](https://forums.suse.com/t/load-balancer-or-service-link/4719/2 "2016-11-28T06:58:13Z")

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Depending on the client behavior, the answer is somewhere between “does not balance properly at all” and “works ok as a simple way to coarsely balance requests”.

The DNS server will return an answer with _all_ of the IPs of the (healthy) `backend` containers in random order each time it asked, with a TTL of 1 second.

But the client is free to do whatever it likes with this information. Some will take just the first answer, others pick randomly from the list, or [not so randomly](https://github.com/rancher/rancher/issues/3495). Some will respect the TTL, others will cache the value for some amount of time they decide, or forever, or until a request fails, etc.

Nginx specifically will resolve names exactly once on startup by default. To make it do anything else you have to give it a [resolver](http://nginx.org/en/docs/http/ngx_http_core_module.html#resolver). The Rancher DNS service is always `169.254.169.250` on any host.

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**Author:** ![twoeo](https://avatars.discourse-cdn.com/v4/letter/t/c5a1d2/32.png) [@twoeo](https://forums.suse.com/u/twoeo)\
**Post date:** [November 28, 2016, 7:22am UTC](https://forums.suse.com/t/load-balancer-or-service-link/4719/3 "2016-11-28T07:22:52Z")

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Thanks vincent.  
Very detailed and clear.

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**Author:** ![twoeo](https://avatars.discourse-cdn.com/v4/letter/t/c5a1d2/32.png) [@twoeo](https://forums.suse.com/u/twoeo)\
**Post date:** [November 28, 2016, 7:28am UTC](https://forums.suse.com/t/load-balancer-or-service-link/4719/4 "2016-11-28T07:28:25Z")

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And in addition, as the nginx example.  
If not give it a resolver, assum that it resolve names as `backend_1`.  
Once `backend_1` is down, it would never switch to `backend_2` or `backend_3` automatically.

So because of

> Depending on the client behavior …

Can I think that it isn’t properly for high availability if only use service link?