| authors | state |
|---|---|
Robert Mustacchi <[email protected]>, Cody Mello <[email protected]> |
publish |
A growing trend in network design is to design the physical topology of the network such that all the machines in a given rack are part of their own broadcast domain. In those worlds, each rack basically uses its own layer three network and VLAN. This may look something like:
Rack 100 Rack 150 Rack 200
VLAN 100 VLAN 150 VLAN 200
L3 192.168.100.0/24 L3 192.168.150.0/24 L3 192.168.200.0/24
+----------------------+ +----------------------+ +----------------------+
| TOR | | TOR | | TOR |
+----------------------+ +----------------------+ +----------------------+
| CN: 192.168.100.4/24 | | CN: 192.168.150.4/24 | | CN: 192.168.200.4/24 |
+----------------------+ +----------------------+ +----------------------+
| CN: 192.168.100.5/24 | | CN: 192.168.150.5/24 | | CN: 192.168.200.5/24 |
+----------------------+ +----------------------+ +----------------------+
| CN: 192.168.100.7/24 | | CN: 192.168.150.7/24 | | CN: 192.168.200.7/24 |
+----------------------+ +----------------------+ +----------------------+
| CN: 192.168.100.8/24 | | CN: 192.168.150.8/24 | | CN: 192.168.200.8/24 |
+----------------------+ +----------------------+ +----------------------+
| CN: 192.168.100.9/24 | | CN: 192.168.150.9/24 | | CN: 192.168.200.9/24 |
+----------------------+ +----------------------+ +----------------------+
| ... | | ... | | ... |
+----------------------+ +----------------------+ +----------------------+
Note how each rack in the example there has its own VLAN and its own L3 network. To communicate between the racks, routing is employed and generally the top of rack switches (TOR) advertise the summarized prefix. While these examples are focused on IPv4, the same can logically be said for IPv6.
Today, Triton network pools are used as a way of joining together multiple disjoint L3 networks which provide a common set of resources. The most common use case for a network pool is for something like an 'external' pool, whereby an organization groups together their disjoint sets of public IP addresses into one pool.
The use of a network pool is very useful. It allows us to give users something for provisioning that will be a constant and work as the availability of the networks that make up the pool come and go.
Today the primary constraint on a network pool is that all of the networks in the pool must have the same NIC tag. In SmartOS and Triton, NIC tags are a way of assigning a name to a physical network and marking which NICs are on it. This allows configuring VMs with the name of the physical network they should be on instead of a Compute Node's MAC address or the name of a NIC.
The reason for this constraint is largely due to where it comes in the provisioning process and what the network pool currently represents. The general idea of a network pool today is that any of the networks in the pool should be interchangeable when considering provisioning. This is enforced by requiring that each network have the same NIC tag.
While the existing networking pool abstraction is very useful, it breaks down in the face of customers who are using topologies as described in the introduction. Since a NIC tag describes a set of connected resources at the physical level, a given NIC tag may only span a given rack.
Because of this, we cannot construct network pools in such topologies that can span multiple racks as the NIC tags are not equivalent nor should they be in this world.
What we want is a way to use network pools where, rather than simply assuming that every network is interchangeable, we instead say that after we pick a given CN for provisioning we pick a specific, compatible network from this set. In other words, the pool can be made up of networks that are bound to specific racks. When a rack is selected for provisioning then the set of networks is whittled down to those which are available on that rack, and an IP provision is attempted on each one.
This work will require changes to both DAPI and NAPI, and changes to VMAPI's workflows to take advantage of their new behaviour.
NAPI will need to return a nic_tags_present array on network pools to
indicate the union of all contained networks' tags. Using this
information, DAPI's server selection logic will need to determine which
servers provide all of the NIC tags needed to satisfy at least one of
the networks from each pool that is being provisioned on.
Once the decision is made, the VMAPI workflow will provision the NIC
with a nic_tags_available field, which will contain a list of all of
the NIC tags present on the selected CN. This will allow NAPI to try
multiple possible solutions when networks are full.
Consider an attempt to provision a VM with two NICs, each one on a different network pool:
[root@headnode (coal) ~]# sdc-napi /network_pools/232074d4-ca09-c15c-b5ee-d836de76514d | json -H
{
"family": "ipv4",
"uuid": "232074d4-ca09-c15c-b5ee-d836de76514d",
"name": "external",
"description": "Internet-accessible networks",
"networks": [
"e1d9e935-4cfb-4d55-b968-2ff7c8470ffe",
"8bf3b871-2888-469d-97f5-910ca8ba7ec5",
"af7e657a-3a01-488f-9002-957ceb02bcf9",
"56198bc6-6a0d-4286-ba4b-2b295cd27ab3",
"ede0ebea-5288-4d16-a405-da86c21a6547"
],
"nic_tag": "r1external",
"nic_tags_present": [
"r1external",
"r2external",
"r3external"
]
}
[root@headnode (coal) ~]# sdc-napi /network_pools/ef8ac216-4205-cd47-a839-bd4e269dc6c3 | json -H
{
"family": "ipv4",
"uuid": "673603c1-38c6-4db1-acb7-a7b51f6469c3",
"name": "internal",
"description": "DC-internal networks",
"networks": [
"7434e9cd-f887-49f5-8e22-4121cb628344",
"46a357de-e875-4ee9-a46f-5e6375f04e86",
"25a2969e-02ba-4dc3-aeec-28f1884ee66d"
],
"nic_tag": "r1internal",
"nic_tags_present": [
"r1internal",
"r2internal",
"r3internal"
]
}
VMAPI would pass this information to DAPI, which would then look for a
server that is on one of the NIC tags from each network pool. In this
example, where each NIC tag corresponds to a network classified as
internal or external in each rack, DAPI might find servers that match
"r1external"/"r1internal", "r2external"/"r2internal", or
"r3external"/"r3internal".
At this point, DAPI would pick a matching server, whose NIC tags might
be "r1internal", "r1external", "admin", "sdc_underlay", and
"sdc_overlay". VMAPI would send this set of tags to NAPI in the
nic_tags_available field for both NICs that it's provisioning. When
considering the set of networks in the pools, it'll select those that
are on "r1internal" and "r1external", and ignore those that are on
other racks.
If all networks in the pool for the provided NIC tags are full, then the NIC provision will fail, and an operator will need to either create additional networks for that NIC tag and add them to the pool or remove the full networks to stop attempts to provision on them.
See DAPI-340, NAPI-403, and ZAPI-781 for the work done to implement the logic described above.
If VMAPI and CNAPI are upgraded ahead of NAPI, then network pools with
mixed NIC tags cannot be created, and the APIs can behave in the same
way that they do today. If, however, NAPI is upgraded ahead of VMAPI and
CNAPI, it would be possible for someone to create a network pool with
mixed tags, and try to provision on it. In this case, NAPI would not
receive the nic_tags_available array, and would not be able to safely
select which networks can be used on the destination CN. NAPI would then
fail NIC provisions on this pool until VMAPI and CNAPI are upgraded to
new enough versions.