The install_asm script calls istioctl install to deploy the Anthos Service Mesh
control plane components (istiod and istio-ingressgateway) for installs,
upgrades, and Istio migrations. Because the script uses istioctl install, if
you need to customize Anthos Service Mesh to
enable an optional feature, you
have to reinstall the control plane with the new configuration.
A change was made to the install_asm script so that you can reinstall
the same version of Anthos Service Mesh. When you reinstall the same version to enable
an optional feature, the existing control plane configuration is overwritten.
Because of this, if you customized the existing installation, you need to
include the same --option and/or --custom_overlay options from
from the previous installation and the --option and/or --custom_overlay
options for the feature(s) that you want to enable or configure.
If you specify more than one IstioOperator custom resource (CR) in a YAML
file, install_asm splits the file into multiple temporary YAML files, one for
each CR. The script splits the CRs into separate files because
istioctl install only applies the first CR in a YAML file containing more than
one CR.
When you reinstall the same version, you specify --mode install just like for
new installations. For information on installing using the script, see
Installing Anthos Service Mesh.