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Using deterministic upgrades through versioned repositories - Amazon Linux 2027
Using a deterministic upgraded systemSelective update of a deterministic upgraded systemUsing persistent override with deterministic upgrade

Using deterministic upgrades through versioned repositories

AL2027 Preview

AL2027 is currently available for preview. It is intended for evaluation and testing only and is not recommended for production workloads.

Using a deterministic upgraded system

Deterministic upgrades let you test every change before it reaches production. Each AL2027 AMI is locked to a specific release, so instances launched from it start with the same package versions. In-place updates target a specific release version, so the same tested set of changes rolls out across a fleet. Test each new AMI or release version in your CI/CD pipeline before deployment. This catches issues before they reach production.

When you run the dnf upgrade command, the system checks for upgrades in the repository version that the releasever variable specifies. A valid releasever is either latest or a date-stamped version such as 2027.0.20260817. The following methods determine the value of releasever, in descending priority. Method 1 overrides methods 2 and 3, and method 2 overrides method 3.

  1. The command line flag --releasever=version, if it's used.

  2. The value in the override variable file /etc/dnf/vars/releasever, if it's set.

  3. The currently installed version of the system-release package.

To see the release version your system is locked to, query the system-release package. In the following example, the system is locked to the 2027.0.20260803 release:

rpm -q system-release
system-release-2027.0.20260803-1.amzn2027.noarch

In a newly installed system, the override variable file /etc/dnf/vars/releasever does not exist, so the system is locked to the installed version of system-release. Because the locked release is immutable, running sudo dnf upgrade on an up-to-date system makes no changes:

sudo dnf upgrade
Updating and loading repositories:
Repositories loaded.
Nothing to do.

To upgrade to a specific release version, pass it with the --releasever option:

sudo dnf upgrade --releasever=2027.0.20260817
Updating and loading repositories:
 Amazon Linux 2027 repository           100% |  11.7 MiB/s |   2.4 MiB |  00m00s
Repositories loaded.
Package                                   Arch   Version                      Repository       Size
Upgrading:
 amazon-linux-repo-cdn                    noarch 0:2027.0.20260817-2.amzn2027 amazonlinux   1.1 KiB
   replacing amazon-linux-repo-cdn        noarch 0:2027.0.20260803-1.amzn2027 amazonlinux   1.1 KiB
 krb5-libs                                x86_64 0:1.22.2-6.amzn2027          amazonlinux   2.4 MiB
   replacing krb5-libs                    x86_64 0:1.22.2-1.amzn2027          amazonlinux   2.4 MiB

   ... [ list edited for clarity ]

 openssl                                  x86_64 1:3.5.7-2.amzn2027           amazonlinux   1.8 MiB
   replacing openssl                      x86_64 1:3.5.5-3.amzn2027           amazonlinux   1.8 MiB

   ... [ list edited for clarity ]

 system-release                           noarch 0:2027.0.20260817-2.amzn2027 amazonlinux  15.6 KiB
   replacing system-release               noarch 0:2027.0.20260803-1.amzn2027 amazonlinux  15.6 KiB
 systemd                                  x86_64 0:260.1-11.amzn2027.0.8      amazonlinux  13.3 MiB
   replacing systemd                      x86_64 0:260.1-11.amzn2027.0.7      amazonlinux  13.3 MiB

   ... [ list edited for clarity ]

Transaction Summary:
 Upgrading:         23 packages
 Replacing:         23 packages

Total size of inbound packages is 28 MiB. Need to download 28 MiB.
After this operation, 81 KiB will be freed (install 102 MiB, remove 102 MiB).

Because the --releasever option overrides both system-release and /etc/dnf/vars/releasever, this upgrade does the following:

  1. Replaces all installed packages that changed between the previous and new versions.

  2. When the target release contains a newer system-release package, the transaction includes it, which locks the system to the new release for all future dnf operations.

By always specifying which AL2027 release to update to, you get a deterministic set of changes across a fleet: you launched version A, updated to B, and then updated to C.

Selective update of a deterministic upgraded system

Note

We recommend installing all updates in a new release rather than selecting specific updates. Applying only part of an update should be the exception, not standard practice. For restricting updates to those from a specific security advisory, see Applying security updates in-place.

You might want to install selected packages from a newer release while leaving the system locked to the original release version. First, identify the packages that you want to upgrade:

sudo dnf check-update --releasever=latest
Updating and loading repositories:
 Amazon Linux 2027 repository           100% |   6.6 MiB/s |   2.4 MiB |  00m00s
Repositories loaded.
Upgrades
amazon-linux-repo-cdn.noarch        2027.0.20260817-2.amzn2027 amazonlinux
krb5-libs.x86_64                    1.22.2-6.amzn2027          amazonlinux
libssh.x86_64                       0.12.2-1.amzn2027          amazonlinux
libssh-config.noarch                0.12.2-1.amzn2027          amazonlinux
openldap.x86_64                     2.6.13-3.amzn2027          amazonlinux
openssh.x86_64                      9.9p1-28.amzn2027          amazonlinux
openssh-clients.x86_64              9.9p1-28.amzn2027          amazonlinux
openssl.x86_64                      1:3.5.7-2.amzn2027         amazonlinux
openssl-fips-provider-latest.x86_64 1:3.5.7-2.amzn2027         amazonlinux
openssl-libs.x86_64                 1:3.5.7-2.amzn2027         amazonlinux
python-unversioned-command.noarch   3.14.5-2.amzn2027.0.4      amazonlinux
python3.x86_64                      3.14.5-2.amzn2027.0.4      amazonlinux
python3-libs.x86_64                 3.14.5-2.amzn2027.0.4      amazonlinux
qrencode-libs.x86_64                4.1.1-3.amzn2027.0.2       amazonlinux
system-release.noarch               2027.0.20260817-2.amzn2027 amazonlinux
systemd.x86_64                      260.1-11.amzn2027.0.8      amazonlinux
systemd-libs.x86_64                 260.1-11.amzn2027.0.8      amazonlinux
systemd-networkd.x86_64             260.1-11.amzn2027.0.8      amazonlinux
systemd-pam.x86_64                  260.1-11.amzn2027.0.8      amazonlinux
systemd-resolved.x86_64             260.1-11.amzn2027.0.8      amazonlinux
systemd-shared.x86_64               260.1-11.amzn2027.0.8      amazonlinux
systemd-sysusers.x86_64             260.1-11.amzn2027.0.8      amazonlinux
systemd-udev.x86_64                 260.1-11.amzn2027.0.8      amazonlinux

Then upgrade only those packages by naming them. Naming specific packages keeps the system-release package, and therefore the version lock, unchanged. The transaction includes related packages that the named packages require at the same version, such as openssl-fips-provider-latest here:

sudo dnf upgrade --releasever=latest openssl openssl-libs
Updating and loading repositories:
Repositories loaded.
Package                                   Arch   Version            Repository       Size
Upgrading:
 openssl                                  x86_64 1:3.5.7-2.amzn2027 amazonlinux   1.8 MiB
   replacing openssl                      x86_64 1:3.5.5-3.amzn2027 amazonlinux   1.8 MiB
 openssl-fips-provider-latest             x86_64 1:3.5.7-2.amzn2027 amazonlinux   2.5 MiB
   replacing openssl-fips-provider-latest x86_64 1:3.5.5-3.amzn2027 amazonlinux   2.5 MiB
 openssl-libs                             x86_64 1:3.5.7-2.amzn2027 amazonlinux   6.9 MiB
   replacing openssl-libs                 x86_64 1:3.5.5-3.amzn2027 amazonlinux   6.9 MiB

Transaction Summary:
 Upgrading:          3 packages
 Replacing:          3 packages

Total size of inbound packages is 4 MiB. Need to download 4 MiB.
After this operation, 14 KiB will be freed (install 11 MiB, remove 11 MiB).
Note

Running sudo dnf upgrade --releasever=latest without naming packages updates all packages, including system-release. The system then remains locked to the new system-release version unless you set the persistent override.

Using persistent override with deterministic upgrade

Instead of adding --releasever=latest to each command, you can unlock the system by setting the variable file to latest. This reverts AL2027 to the AL2 update model, where every package manager invocation uses the latest release and does not lock to any specific version of the OS:

echo latest | sudo tee /etc/dnf/vars/releasever
latest
Warning

Unlocking the package manager with a persistent override removes the ability to test an OS update before it reaches production. A new AL2027 release can happen at any point in time, so all uses of latest in production carry the risk of discovering an incompatibility between your application and an OS update in production.

To restore the default locking behavior, remove the override file:

sudo rm /etc/dnf/vars/releasever

Rather than disabling deterministic upgrades, we recommend replacing instances with ones launched from a new AMI. If instance replacement is not an option, use tools such as AWS Systems Manager Patch Manager to orchestrate applying updates across a fleet, or EC2 Image Builder to automatically build, patch, and test your own AMIs derived from AL2027 base images.