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Bug 1835867

Summary: AWS: installer is leaving unused network ranges when it shouldn't
Product: OpenShift Container Platform Reporter: Abhinav Dahiya <adahiya>
Component: InstallerAssignee: Abhinav Dahiya <adahiya>
Installer sub component: openshift-installer QA Contact: Yunfei Jiang <yunjiang>
Status: CLOSED ERRATA Docs Contact:
Severity: medium    
Priority: medium CC: tsze, yunjiang
Version: 4.5   
Target Milestone: ---   
Target Release: 4.5.0   
Hardware: Unspecified   
OS: Unspecified   
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Clone Of: Environment:
Last Closed: 2020-07-13 17:38:54 UTC Type: Bug
Regression: --- Mount Type: ---
Documentation: --- CRM:
Verified Versions: Category: ---
oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
Cloudforms Team: --- Target Upstream Version:
Embargoed:
Bug Depends On:    
Bug Blocks: 1836982    

Description Abhinav Dahiya 2020-05-14 16:05:07 UTC
Description of problem:

When trying to create a cluster with,
- machineNetwork: 10.0.0.0/16
- only one AZ ca-central-1b
the installer creates subnets with 10.0.0.0/20 and  10.0.128.0/20.
With this setup only 4096*2 machines can be created. and the rest of the VPC range is left completely used. This is esp problematic for smaller machineNetworks.

The installer should have created the subnets with 10.0.0.0/17 and 10.0.128.0/17 ranges.

example of the install-config.yaml used.
```
apiVersion: v1
baseDomain: XXXXXX
controlPlane:
  name: master
  replicas: 3
  platform:
    aws:
      zones:
      - ca-central-1b
compute:
- name: worker
  replicas: 3
  platform:
    aws:
      zones:
        - ca-central-1b
metadata:
  name: xxxxx
networking:
  machineNetwork:
  - cidr: 10.0.0.0/16
platform:
  aws:
    region: ca-central-1
```

Comment 3 errata-xmlrpc 2020-07-13 17:38:54 UTC
Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.

For information on the advisory, and where to find the updated
files, follow the link below.

If the solution does not work for you, open a new bug report.

https://access.redhat.com/errata/RHBA-2020:2409

Comment 4 To Hung Sze 2021-01-29 17:27:14 UTC
Just capturing results from my test run just now with 4.7 fc4:

Started with
compute:
- architecture: amd64
  hyperthreading: Enabled
  name: worker
  platform: 
    aws:
      zones:
      - us-east-2b 
  replicas: 3
controlPlane:
  architecture: amd64
  hyperthreading: Enabled
  name: master
  platform:  
    aws:
      zones:
      - us-east-2b
  replicas: 3
...
networking:
  clusterNetwork:
  - cidr: 10.128.0.0/14
    hostPrefix: 23
  machineNetwork:
  - cidr: 10.0.0.0/16
  networkType: OpenShiftSDN
  serviceNetwork:
  - 172.30.0.0/16
platform:
  aws:
    region: us-east-2 

Ends with two subnets:
tszeaws012921b-674lr-public-us-east-2b     10.0.0.0/17
tszeaws012921b-674lr-private-us-east-2b    10.0.128.0/17

It also doesn't apply to GCP as GCP uses one subnet across all zones (AWS needs different subnets for each zone).