~themue/clouddocs/009-openstack

Title: Scaling - OpenStack

Status: In Progress

# Scaling - OpenStack

## Introduction

Whereas traditional applications required larger hardware to scale ("vertical scaling"), 

cloud-based applications typically request more, discrete hardware ("horizontal scaling"). 

If your cloud is successful, eventually you must add resources to meet the increasing 

demand.

To suit the cloud paradigm, OpenStack itself is designed to be horizontally scalable. 

Rather than switching to larger servers, you procure more servers and simply install 

identically configured services. Ideally, you scale out and load balance among groups 

of functionally identical services.

But to scale the services running on OpenStack sometimes even OpenStack itself has to

be scaled. This means nodes for computing or storage have to be added.

## Scope

**TODO**

## Nova

### Analyzis

To list the hosts and the nova-related services that run on them call

```

$ nova host-list

+------------------+-------------+----------+

| host_name        | service     | zone     |

+------------------+-------------+----------+

| devstack-grizzly | conductor   | internal |

| devstack-grizzly | compute     | nova     |

| devstack-grizzly | cert        | internal |

| devstack-grizzly | network     | internal |

| devstack-grizzly | scheduler   | internal |

| devstack-grizzly | consoleauth | internal |

+------------------+-------------+----------+

```

To get a summary of resource usage of all of the instances running on the host call

```

$ nova host-describe devstack-grizzly

+------------------+----------------------------------+-----+-----------+---------+

| HOST             | PROJECT                          | cpu | memory_mb | disk_gb |

+------------------+----------------------------------+-----+-----------+---------+

| devstack-grizzly | (total)                          | 2   | 4003      | 157     |

| devstack-grizzly | (used_now)                       | 3   | 5120      | 40      |

| devstack-grizzly | (used_max)                       | 3   | 4608      | 40      |

| devstack-grizzly | b70d90d65e464582b6b2161cf3603ced | 1   | 512       | 0       |

| devstack-grizzly | 66265572db174a7aa66eba661f58eb9e | 2   | 4096      | 40      |

+------------------+----------------------------------+-----+-----------+---------+

```

These information help you understand how this host is used.

- The `cpu` column shows the sum of the virtual CPUs for instances running on the host.

- The `memory_mb` column shows the sum of the memory (in MB) allocated to the instances 

  that run on the hosts.

- The `disk_gb` column shows the sum of the root and ephemeral disk sizes (in GB) of 

  the instances that run on the hosts.

- The `used_now` row shows the sum of the resources allocated to the instances that run 

  on the host plus the resources allocated to the virtual machine of the host itself.

- The `used_max` row shows the sum of the resources allocated to the instances that run 

  on the host.

**Note:** These values are computed by using only information about the flavors of the 

instances that run on the hosts. This command does not query the CPU usage, memory usage, 

or hard disk usage of the physical host.

Now you an retrieve the CPU, memory, I/O, and network statistics for an instance. First

list all instances.

```

$ nova list

+--------------------------------------+----------------------+--------+------------+-------------+------------------+

| ID                                   | Name                 | Status | Task State | Power State | Networks         |

+--------------------------------------+----------------------+--------+------------+-------------+------------------+

| 84c6e57d-a6b1-44b6-81eb-fcb36afd31b5 | myCirrosServer       | ACTIVE | None       | Running     | private=10.0.0.3 |

| 8a99547e-7385-4ad1-ae50-4ecfaaad5f42 | myInstanceFromVolume | ACTIVE | None       | Running     | private=10.0.0.4 |

+--------------------------------------+----------------------+--------+------------+-------------+------------------+

```

Then, get diagnostic statistics:

```

$ nova diagnostics myCirrosServer

+------------------+----------------+

| Property         | Value          |

+------------------+----------------+

| vnet1_rx         | 1210744        |

| cpu0_time        | 19624610000000 |

| vda_read         | 0              |

| vda_write        | 0              |

| vda_write_req    | 0              |

| vnet1_tx         | 863734         |

| vnet1_tx_errors  | 0              |

| vnet1_rx_drop    | 0              |

| vnet1_tx_packets | 3855           |

| vnet1_tx_drop    | 0              |

| vnet1_rx_errors  | 0              |

| memory           | 2097152        |

| vnet1_rx_packets | 5485           |

| vda_read_req     | 0              |

| vda_errors       | -1             |

+------------------+----------------+

```

Finally you can get summary statistics for each tenant.

```

$ nova usage-list

Usage from 2013-06-25 to 2013-07-24:

+----------------------------------+-----------+--------------+-----------+---------------+

| Tenant ID                        | Instances | RAM MB-Hours | CPU Hours | Disk GB-Hours |

+----------------------------------+-----------+--------------+-----------+---------------+

| b70d90d65e464582b6b2161cf3603ced | 1         | 344064.44    | 672.00    | 0.00          |

| 66265572db174a7aa66eba661f58eb9e | 3         | 671626.76    | 327.94    | 6558.86       |

+----------------------------------+-----------+--------------+-----------+---------------+

```

**TODO** How to interpret this information to know when to scale?

### Scaling

Adding compute nodes is straightforward. They are easily picked up by the existing 

installation. Simply call

```

juju add-unit nova-compute

```

## Cinder

**TODO**