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We're currently rebuilding our platform into a microservice architecture and we've been looking into Azure Container Service as an infrastructure solution for working with Docker containers, but I'm afraid this stuff is a little out of my wheelhouse at the moment.

From the site, it explains 'Masters' as what orchestrates the VMs and the agents are what do the computing. It also says that a minimum of 3 VMs are required for each cluster: the Master, a public agent, and a private agent. So a few questions here:

  • What is the difference between a public and private agent and what does that mean to me as a developer?

  • When would I want to purchase another master?

  • When would I want to purchase more agents? Do I need more private agents, or is that just a one time thing to meet the minimum requirement?

  • There are two concepts here (master and agent), so which ones are involved with scaling under what circumstances? (maybe this gets answered by the previous two questions)

TIA

Sinaesthetic
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1 Answers1

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Q1: Private agent nodes run through a non-routable network. This network is only accessible from the admin zone or through the public zone edge router. By default, DC/OS launches apps on private agent nodes.

Public agent nodes run DC/OS apps and services through a publicly accessible network.

Q2: 1 master is fine for testing and workloads that are not mission critical. If it fails existing workloads will continue to run but you will not be able to schedule more workloads or ensure existing workloads continue to run. You will restart the master and, with luck, it will rebuild it's state and all will be good. But if the data is corrupted or similar you will have work to do.

3 masters are fine for most cases. If one fails you will continue to operate as normal, when you bring that one back up the other two will have agreed on the current state and everything will converge. If you lose two you will still probably be OK (see above). If you lose all three then you are in the same state as above.

5 masters just makes things safer still.

The reason for the odd number is that under normal circumstances the masters elect a leader, so you need an odd number.

Q3: You have as many agents as you need for your workloads. If you need more public compute capacity, add more cores to the public pool. Ditto the private pool.

Q4: Agents are where you scale in normal circumstances

rgardler
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