How/where is Bottlerocket OS Image disk size determined?

[rajivr]

I just managed to boot metal-dev variant on QEMU.

I noticed that the generated raw image (bottlerocket-metal-dev-x86_64-1.30.0-00000000.img.lz4) was 3GiB in size.

$ sgdisk -p bottlerocket-metal-dev-x86_64-1.30.0-00000000.img
Disk bottlerocket-metal-dev-x86_64-1.30.0-00000000.img: 6291456 sectors, 3.0 GiB
Sector size (logical): 512 bytes
Disk identifier (GUID): C3110493-C15C-4CFB-8C64-464A5D1FF74A
Partition table holds up to 128 entries
Main partition table begins at sector 2 and ends at sector 33
First usable sector is 34, last usable sector is 6291422
Partitions will be aligned on 2048-sector boundaries
Total free space is 6077 sectors (3.0 MiB)

Number  Start (sector)    End (sector)  Size       Code  Name
   1            2048           10239   4.0 MiB     EF02  BIOS-BOOT
   2           10240           20479   5.0 MiB     EF00  EFI-SYSTEM
   3           20480          102399   40.0 MiB    FFFF  BOTTLEROCKET-BOOT-A
   4          102400         1986559   920.0 MiB   FFFF  BOTTLEROCKET-ROOT-A
   5         1986560         2007039   10.0 MiB    FFFF  BOTTLEROCKET-HASH-A
   6         2007040         2058239   25.0 MiB    FFFF  BOTTLEROCKET-RESERV...
   7         2058240         2068479   5.0 MiB     FFFF  EFI-BACKUP
   8         2068480         2150399   40.0 MiB    FFFF  BOTTLEROCKET-BOOT-B
   9         2150400         4034559   920.0 MiB   FFFF  BOTTLEROCKET-ROOT-B
  10         4034560         4055039   10.0 MiB    FFFF  BOTTLEROCKET-HASH-B
  11         4055040         4106239   25.0 MiB    FFFF  BOTTLEROCKET-RESERV...
  12         4106240         4190207   41.0 MiB    FFFF  BOTTLEROCKET-PRIVATE
  13         4190208         6287359   1024.0 MiB  FFFF

However, on AWS AMI (for example aws-eks-1.31-x86_64-1.26.1-943d9a41) the Bottlerocket OS Image disk size is 2GiB.

# sgdisk -p /.bottlerocket/rootfs/dev/nvme0n1
Disk /.bottlerocket/rootfs/dev/nvme0n1: 4194304 sectors, 2.0 GiB
Logical sector size: 512 bytes
Disk identifier (GUID): 546580A1-77FC-47B6-8CC9-C8273E1912B9
Partition table holds up to 128 entries
First usable sector is 34, last usable sector is 4194270
Partitions will be aligned on 2048-sector boundaries
Total free space is 4029 sectors (2.0 MiB)

Number  Start (sector)    End (sector)  Size       Code  Name
   1            2048           10239   4.0 MiB     EF02  BIOS-BOOT
   2           10240           20479   5.0 MiB     EF00  EFI-SYSTEM
   3           20480          102399   40.0 MiB    FFFF  BOTTLEROCKET-BOOT-A
   4          102400         1986559   920.0 MiB   FFFF  BOTTLEROCKET-ROOT-A
   5         1986560         2007039   10.0 MiB    FFFF  BOTTLEROCKET-HASH-A
   6         2007040         2058239   25.0 MiB    FFFF  BOTTLEROCKET-RESERV...
   7         2058240         2068479   5.0 MiB     FFFF  EFI-BACKUP
   8         2068480         2150399   40.0 MiB    FFFF  BOTTLEROCKET-BOOT-B
   9         2150400         4034559   920.0 MiB   FFFF  BOTTLEROCKET-ROOT-B
  10         4034560         4055039   10.0 MiB    FFFF  BOTTLEROCKET-HASH-B
  11         4055040         4106239   25.0 MiB    FFFF  BOTTLEROCKET-RESERV...
  12         4106240         4190207   41.0 MiB    FFFF  BOTTLEROCKET-PRIVATE
  13         4190208         4192255   1024.0 KiB  FFFF

I was wondering where/how the Bottlerocket OS disk image size is set? I looked at bottlerocket-1.30.0/variants/{aws-k8s-1.31,metal-dev}/Cargo.toml. There does not seem to be an option to set the disk size there.

[yeazelm]

Metal and VMware images use the unified partition layout. That last partition (13 4190208 6287359 1024.0 MiB FFFF) is the BOTTLEROCKET-DATA partition that is a second volume with the AMIs. There is a tiny partition there that can be used in specific situations on AWS but the 13th partition will essentially not be touched and remain as small as possible for the AMIs. On the unified disk images, that 1GB partition will be resized on first boot to fill the disk and be used for data. This link in rpm2img has a bit more info on how these work.

[rajivr]

Thanks for the quick reply @yeazelm . Appreciate it!