Configuring SNAT

Restricting an SNAT IP Pool to Specific Kubernetes Namespaces or TAS Orgs

You can specify which Kubernetes namespace or TAS org can be allocated IPs from the SNAT IP pool by adding the following tags to the IP pool.

For a Kubernetes namespace: scope: ncp/owner, tag: ns:<namespace_UUID>
For a TAS org: scope: ncp/owner, tag: org:<org_UUID>

You can get the namespace or org UUID with one of the following commands:

kubectl get ns -o yaml
cf org <org_name> --guid

Note the following:

Each tag should specify one UUID. You can create multiple tags for the same pool.
If you change the tags after some namespaces or orgs have been allocated IPs based on the old tags, those IPs will not be reclaimed until the SNAT configurations of the Kubernetes services or TAS apps change or NCP restarts..
The namespace and TAS org owner tags are optional. Without these tags, any namespace or TAS org can have IPs allocated from the SNAT IP pool.

Configuring an SNAT IP Pool for a Service

You can configure an SNAT IP pool for a service by adding an annotation to the service. For example,

    apiVersion: v1
    kind: Service
    metadata:
      name: svc-example
      annotations:
        ncp/snat_pool: <external IP pool ID or name>
      selector:
        app: example
    ...

The IP pool specified by ncp/snat_pool must have the tag scope: ncp/owner, tag: cluster:<cluster_name>.

NCP will configure the SNAT rule for this service. The rule's source IP is the set of backend pods. The destination IP is the SNAT IP allocated from the specified external IP pool. If an error occurs when NCP configures the SNAT rule, the service will be annotated with ncp/error.snat: <error>. The possible errors are:

IP_POOL_NOT_FOUND - The SNAT IP pool is not found in NSX Manager.
IP_POOL_EXHAUSTED - The SNAT IP pool is exhausted.
IP_POOL_NOT_UNIQUE - The pool specified by ncp/snat_pool refers to multiple pools in NSX Manager.
SNAT_RULE_OVERLAPPED - A new SNAT rule is created, but the SNAT service's pod also belongs to another SNAT service, that is, there are multiple SNAT rules for the same pod.
POOL_ACCESS_DENIED - The IP pool specified by ncp/snat_pool does not have the tag scope: ncp/owner, tag: cluster:<cluster_name>, or the pool's owner tag does not match the namespace of the service that is sending the allocation request. After you fix the error, you must restart NCP, or remove the ncp/snat_pool annotation and add it again.

Note the following:

The pool specified by ncp/snat_pool should already exist in NSX before the service is configured.
In NSX, the priority of the SNAT rule for the service is higher than that for the project.
If a pod is configured with multiple SNAT rules, only one will work.
You can change to a different IP pool by changing the annotation and restarting NCP.

Configuring an SNAT IP Pool for a Namespace

You can configure an SNAT IP pool for a namespace by adding an annotation to the namespace. For example,

    apiVersion: v1
    kind: Namespace
    metadata:
      name: ns-sample
      annotations:
        ncp/snat_pool: <external IP pool ID or name>
    ...

NCP will configure the SNAT rule for this namespace. The rule's source IP is the set of backend pods. The destination IP is the SNAT IP allocated from the specified external IP pool. If an error occurs when NCP configures the SNAT rule, the namespace will be annotated with ncp/error.snat: <error>. The possible errors are:

IP_POOL_NOT_FOUND - The SNAT IP pool is not found in NSX Manager.
IP_POOL_EXHAUSTED - The SNAT IP pool is exhausted.
IP_POOL_NOT_UNIQUE - The pool specified by ncp/snat_pool refers to multiple pools in NSX Manager.
POOL_ACCESS_DENIED - The IP pool specified by ncp/snat_pool does not have the tag scope: ncp/owner, tag: cluster:<cluster_name>, or the pool's owner tag does not match the namespace that is sending the allocation request. After you fix the error, you must restart NCP, or remove the ncp/snat_pool annotation and add it again.

Note the following:

You can specify only one SNAT IP pool in the annotation.
The SNAT IP pool does not need to be configured in ncp.ini.
The IP pool specified by ncp/snat_pool must have the tag scope: ncp/owner, tag: cluster:<cluster_name>.
The IP pool specified by ncp/snat_pool can also have a namespace tag scope: ncp/owner, tag: ns:<namespace_UUID>.
If the ncp/snat_pool annotation is missing, the namespace will use the SNAT IP pool for the cluster.
You can change to a different IP pool by changing the annotation and restarting NCP.

Configuring an SNAT IP Address for a Service

You can configure an SNAT IP address for a service by adding an annotation to the service. For example,

    apiVersion: v1
    kind: Service
    metadata:
      name: svc-example
      annotations:
        ncp/static_snat_ip: "1.2.3.4"
    ...

If the annotation ncp/snat_pool is also specified, the SNAT IP address must be in the specified SNAT address pool. Otherwise, it must be in the external IP pool specified in ncp.ini. If there are no errors, NCP will create or update the SNAT rule by using the annotated SNAT IP address for this service. The status of configuring the SNAT rule will be annotated with ncp/snat_ip_status in the service. The possible values are:

IP_ALLOCATED_SUCCESSFULLY
IP_ALREADY_ALLOCATED - The IP address has already been allocated.
IP_NOT_IN_POOL - The IP address is not in the SNAT IP Pool.
IP_POOL_EXHAUSTED - The SNAT IP Pool is exhausted.
SNAT_PROCESS_FAILED - An unknown error occurred.

Configuring an SNAT IP Address for a Namespace

You can configure an SNAT IP address for a namespace by adding an annotation to the namespace. For example,

    apiVersion: v1
    kind: Namespace
    metadata:
      name: svc-example
      annotations:
        ncp/static_snat_ip: "1.2.3.4"
    ...

If the annotation ncp/snat_pool is also specified, the SNAT IP address must be in the specified SNAT address pool. Otherwise, it must be in the external IP pool specified in ncp.ini. If there are no errors, NCP will create or update the SNAT rule by using the annotated SNAT IP address for this namespace. The status of configuring the SNAT rule will be annotated with ncp/snat_ip_status in the namespace. The possible values are:

IP_ALLOCATED_SUCCESSFULLY
IP_ALREADY_ALLOCATED - The IP address has already been allocated.
IP_NOT_IN_POOL - The IP address is not in the SNAT IP Pool.
IP_NOT_REALIZED - An error occurred in NSX.
IP_POOL_EXHAUSTED - The SNAT IP Pool is exhausted.
SNAT_PROCESS_FAILED - An unknown error occurred.

Configuring an SNAT Pool for a TAS App

By default, NCP configures SNAT IP for a TAS (Tanzu Application Service) org. You can configure an SNAT IP for an app by creating an app with a manifest.xml that contains the SNAT IP pool information. For example,

    applications:
      - name: frontend
        memory: 32M
        disk_quota: 32M
        buildpack: go_buildpack
        env:
          GOPACKAGENAME: example-apps/cats-and-dogs/frontend
          NCP_SNAT_POOL: <external IP pool ID or name>
    ...

NCP will configure the SNAT rule for this app. The rule's source IP is the set of instances' IPs and its destination IP is the SNAT IP allocated from an external IP pool. Note the following:

The pool specified by NCP_SNAT_POOL should already exist in NSX before the app is pushed.
The priority of SNAT rule for an app is higher than that for an org.
An app can be configured with only one SNAT IP.
You can change to a different IP pool by changing the configuration and pushing the app again.

Configuring SNAT for TAS version 3

With TAS version 3, you can configure SNAT in one of two ways:

Configure NCP_SNAT_POOL in manifest.yml when creating the app.

For example, the app is called bread and the manifest.yml has the following information:

applications:
- name: bread
  stack: cflinuxfs2
  random-route: true
  env:
    NCP_SNAT_POOL: AppSnatExternalIppool
  processes:
  - type: web
    disk_quota: 1024M
    instances: 2
    memory: 512M
    health-check-type: port
  - type: worker
    disk_quota: 1024M
    health-check-type: process
    instances: 2
    memory: 256M
    timeout: 15

Run the following commands:

cf v3-push bread
cf v3-apply-manifest -f manifest.yml
cf v3-apps
cf v3-restart bread

Configure NCP_SNAT_POOL using the cf v3-set-env command.

Run the following commands (assuming the app is called app3):

cf v3-set-env app3 NCP_SNAT_POOL AppSnatExternalIppool
(optional) cf v3-stage app3 -package-guid <package-guid> (You can get package-guid with "cf v3-packages app3".)
cf v3-restart app3

Configuring an SNAT IP Pool or IP Address for a TAS Org

You can configure an SNAT IP pool or IP address for a TAS Org using the following annotations:

ncp_snat_pool - The pool must exist and have the tag scope: ncp/owner, tag: cluster:<cluster_name>.
ncp_snat_ip - A specific address in an IP pool.

Note the following:

If both ncp_snat_pool and ncp_snat_ip are specified, the SNAT IP address must be in the specified SNAT IP pool.
If only ncp_snat_ip is specified, the SNAT IP address must be in the external IP pool specified in ncp.ini.
If only ncp_snat_pool is specified, the SNAT IP address will be allocated from the specified pool.

You can configure SNAT IP for an org with the cf curl command. For example:

cf curl v3/organizations/<org-guid> -X PATCH  -d '{"metadata": {"annotations": {"ncp_snat_pool": "ann-ip-pool", "ncp_snat_ip": "1.2.3.4"}}}'

You can get org-guid with the following command:

cf org <org-name> --guid

You can remove the ncp_snat_ip annotation with the following command:

cf curl v3/organizations/<org-guid> -X PATCH  -d '{"metadata": {"annotations": {"ncp_snat_ip": null}}}'

You can go to the NSX Manager UI to check if the SNAT rule is successfully created. To check for errors, look at the NCP logs.

If you see the POOL_ACCESS_DENIED error in the NCP log, it means that the IP pool specified by ncp_snat_pool does not have the tag scope: ncp/owner, tag: cluster:<cluster_name>, or the pool's owner tag does not match the org that is sending the allocation request. After you fix the error, you must restart NCP, or remove the ncp_snat_pool annotation and add it again.

SNAT, Container Networks and Gateway Firewall

The following information is applicable to NCP 4.1.2.2 and later.

If SNAT is enabled for Container networks, NCP creates SNAT rules on the top-tier router (also called foundation tier-0 in TAS) in both Manager and Policy modes. In TAS, this is controlled by the Enable SNAT for Container Networks configuration option in the VMware NSX-T tile. In Kubernetes, it is controlled by the configuration option ncp.coe.enable_snat. In TKGI, it is always enabled.

If Gateway Firewall rules are configured on the top tier-0 router, SNAT traffic on the top tier-0 router can be impacted depending on the value of the firewall_match property of the SNAT rule. A key difference between the SNAT rules in Manager and Policy mode is the default value of the property firewall_match in a NAT rule. In Policy mode, the default value is MATCH_INTERNAL_ADDRESS. In Manager mode it is BYPASS. If NCP uses any value other than BYPASS for this option, the Gateway Firewall rules defined on the top tier-0 router will be enforced on NCP-created SNAT rules as well. This implies that the traffic might be dropped if there is no rule to explicitly allow egress traffic from the container range.

Due to the difference in the default behavior of NAT rules, you can configure the firewall_match property of the SNAT rules created by NCP in Policy mode. In TAS, it can be done via the configuration option NAT Firewall Match for SNAT Rules in the VMware NSX-T tile in OpsManager. In Kubernetes, it can be done via the configuration option cfg.CONF.nsx_v3.natfirewallmatch. The available options are:

BYPASS - No change compared to Manager mode. Gateway Firewall is not enforced for traffic that goes through SNAT.
MATCH_INTERNAL_ADDRESS - Default setting. Gateway Firewall is enforced and will match traffic on source addresses before SNAT. You must ensure that rules are in place to allow traffic coming from the container range.
MATCH_EXTERNAL_ADDRESS - Gateway Firewall is enforced and will match traffic on source addresses after SNAT. You must ensure that rules are in place to allow traffic coming from the SNAT range, that is, the external IP pools configured for NCP.

Note that NCP does not update the existing SNAT rules if the value of this configuration option is updated. However, it will update this property if the SNAT rule is updated due to any other reason.

Notes specific to TKGI:

In TKGI, this property can be configured via the cluster network profile.
This property is more relevant to dual-tier topologies. For single-tier topologies you should not create Gateway Firewall rules on cluster tier-1 gateways (even though TKGI does not explicitly state that this is not supported).
In TKGI, the logic is the same with some small differences:
- The "Top Tier" router for a cluster will be a tier-1 router for single-tier topologies, and a tier-0 for dual-tier topologies.
- No SNAT rule is created if the namespace is annotated with ncp/no_snat: true.