Usage

ENTERPRISE

Common commands for Edge-LB usage

This page covers common commands for Edge-LB usage. For a more detailed list of CLI commands, consult the dcos edgelb cli reference.

Prerequisites

Create pools

After launching a service and creating a pool configuration file, you can use the CLI to deploy it:

dcos edgelb create <pool-configuration-file>

Please refer to the tutorials sections for examples of pool configs.

Update pools

Update a pool’s configuration with the following command:

dcos edgelb update <pool-configuration-file>

Scale down Edge-LB pool instances

To scale down Edge-LB pool instances change the count to a lower number. E.g. if the previous count in the Edge-LB pool config was 5, change it to 2.

An Example config file for Edge-LB pool config:

{
  "id": "/my-app",
  ...
  "name": "sample-minimal",
  "count": 2,
  ...
}

Exposing mesos task without pre-defined mesos-assigned ports

This feature allows you to expose task without mesos assigend port.

Prior to this feature, Edge-LB only exposed task that have ports assigned by mesos. Its not a requirement for Mesos tasks to have port assigned always. By leveraging this feature, when there is no port assigned for task, an Operator can specify a port in the pool config to expose that task.

Allow dynamic allocation of the HAProxy Stats port

This feature allows allocating Stats port dynamically if there is more than on pool on an agent node.

Prior to this feature, it wasn’t possible to disable Stats port 9090 for a pool. This results in having only one Edge-LB pool per agent. Thus, it wasn’t possible to deploy two Edge-LB pools on the same agent without manually setting different values for Stats port. By leveraging this feature, multiple pools on the same agent can have Stats port without port conflict.

Allow dynamic allocation of the HAProxy frontend port

This feature allows allocating Frontend port dynamically if there is more than on pool on an agent node.

When a public cloud LB like AWS ELB is sitting in front of Edge-LB, the ELB will handle the proxy/ load-balancing between the Client and Edge-LB pool. In such scenarios having frontend ports doesn’t provide much value. By leveraging this feature, you can have multiple Frontend ports allocated dynamiccaly for multiple Edge-LB pools on the same agent for better resource utilization.

Normal reload scenario

A change to a service (such as scaling up) that is load balanced by a pool will trigger a reload of its load balancers. This reload has the following properties:

  • No traffic is dropped (unless the service instance that was serving the request was killed).

  • The load balancer will keep the long-running connections intact, while all the new connections will be proxied using the new configuration.

  • A reload will occur at most once every 3 seconds.

The properties of this reload enable strategies like Blue/Green Deployment.

Load balancer relaunch scenario

A change to the load balancer pool (such as adding a secret) will trigger a relaunch of all load balancers in the pool. This relaunch has the following properties:

  • Traffic currently flowing through the given load balancer is dropped when it is stopped. To minimize the impact, we suggest running more than one load balancer within the pool.
  • Only one load balancer is stopped in the pool during the update at a time.
  • The load balancer will be relaunched on the same node (unless the node itself has failed).

WARNING: The number of instances of load balancers cannot be scaled down. This limitation will be addressed in a future Edge-LB release.

Replacing a failed pod

By default, Edge-LB load balancer instances are tied to a given node; when the node goes down, Edge-LB does not automatically relocate the pod containing the Edge-LB load balancer instance to a new node. You must issue a pod replace command to the pool scheduler to tell it to start the load balancer instance on a new node. If a machine hosting a pod is permanently lost, manual intervention is required to discard the missing pod and start it on a new node.

This can all be done using the dcos CLI edgelb-pool subcommand (note that this is distinct from the edgelb subcommand, and must be installed separately if it has not yet been installed).

  1. Install the edgelb-pool CLI subcommand:
$ dcos package install edgelb-pool --cli --yes
  1. Get the name of the pool that owns the pod you need to relocate:
$ dcos edgelb list

This should show all pool configurations. The pool that has a missing pod will be your value for <pool-name> below.

  1. Get the name of the pod you need to replace (the one that was running on the removed public agent). This will be your value for <pod-id>.
$ dcos edgelb-pool --name=/dcos-edgelb/pools/<pool-name> pod list
  1. Use <pod-id> with the pod replace command:
$ dcos edgelb-pool --name=/dcos-edgelb/pools/<pool-name> pod replace <pod-id>

This will destroy the pool server and re-launch a new one on the new public agent.

For a list of Edge-LB commands, see the CLI Reference page.