GCP - how to change the IP on a VM with 2 NICs? - google-cloud-platform

Question

I have a VM with 2 NICs. For all intents and purposes, it's a VPN server that takes connection requests on one interface and then forwards traffic out to the other interface.
Periodically, I need to change the IP on the second interface, which is easily done via the web interface. I'd like to make this change using GCP scripting tools to make the process less manual.
I have managed to automate all steps except updating the access-config. This is because both interfaces have the same access-config name ("External NAT"). I've been unable to find a way to rename or recreate this access-config name, nor have I found any workaround.
Any input would be greatly appreciated.
- accessConfigs:
- kind: compute#accessConfig
name: External NAT
natIP: ##.##.##.##
networkTier: STANDARD
type: ONE_TO_ONE_NAT
fingerprint: ==========
kind: compute#networkInterface
name: nic0
network: https://www.googleapis.com/compute/v1/projects/#######/global/networks/inbound
networkIP: 10.#.#.#
subnetwork: https://www.googleapis.com/compute/v1/projects/#######/regions/northamerica-northeast1/subnetworks/inbound
- accessConfigs:
- kind: compute#accessConfig
name: External NAT
natIP: ##.##.##.##
networkTier: STANDARD
type: ONE_TO_ONE_NAT
fingerprint: =========
kind: compute#networkInterface
name: nic1
network: https://www.googleapis.com/compute/v1/projects/#######/global/networks/outbound
networkIP: 10.0.2.3
subnetwork: https://www.googleapis.com/compute/v1/projects/#######/regions/northamerica-northeast1/subnetworks/outbound

Answer 1

I believe (!?) [really am not certain] that you must delete and then create; you can't update an existing access config to change the IP using gcloud.
Someone else please confirm!
PLEASE try this on a sacrificial instance before you use it on the production instance
Thus:
PROJECT=[[YOUR-PROJECT]]
ZONE=[[YOUR-ZONE]]
INSTANCE=[[YOUR-INSTANCE]]
INTERFACE=[[YOUR-INTERFACE]] # Perhaps "nic1"
# Show what we have currently
gcloud compute instances describe ${INSTANCE} \
--zone=${ZONE} --project=${PROJECT} \
--format="yaml(networkInterfaces)"
# Delete the "External NAT" for ${INTERFACE}
gcloud compute instances delete-access-config instance-1 \
--zone=${ZONE} --project=${PROJECT} \
--network-interface=${INTERFACE} \
--access-config-name="External NAT"
# Show what we have currently **without** "External NAT" for ${INTERFACE}
gcloud compute instances describe ${INSTANCE} \
--zone=${ZONE} --project=${PROJECT} \
--format="yaml(networkInterfaces)"
# Create a new "External NAT" for ${INTERFACE}
# Include --address=ADDRESS if you have one
gcloud compute instances add-access-config ${INSTANCE} \
--zone=${ZONE} --project=${PROJECT} \
--network-interface=${INTERFACE} \
--access-config-name="External NAT"
# Show what we have currently with a **new** "External NAT" for ${INTERFACE}
gcloud compute instances describe ${INSTANCE} \
--zone=${ZONE} --project=${PROJECT} \
--format="yaml(networkInterfaces)"
Update
This was bugging me.
You can filter in the describe commands by ${INTERACE} value:
gcloud compute instances describe ${INSTANCE} \
--zone=${ZONE} --project=${PROJECT} \
--format="yaml(networkInterfaces[].filter(name:${INTERFACE})"
Because gcloud has proprietary filtering|formatting, it's often better to format as JSON and then use jq. Using jq, we can filter by ${INTERFACE} and return only the 'External NAT` access config:
gcloud compute instances describe ${INSTANCE} \
--zone=${ZONE} --project=${PROJECT} \
--format="json" \
jq -r ".networkInterfaces[]|select(.name==\"${INTERFACE}\")|.accessConfigs[]|select(.name==\"External NAT\")"