Support overwriting bootstrap scripts (#1174)

[ci]

fixes #1170

Signed-off-by: Moritz Kiefer <moritz.kiefer@purelyfunctional.org>
Co-authored-by: Moritz Kiefer <moritz.kiefer@purelyfunctional.org>

Author: moritzkiefer-da

cluster/images/common/entrypoint.sh

@@ -27,6 +27,11 @@ if [ -f /app/pre-bootstrap.sh ]; then
   source /app/pre-bootstrap.sh
 fi
 
+if [ -n "${OVERRIDE_BOOTSTRAP_SCRIPT:-}" ]; then
+  json_log "Overwriting bootstrap script from environment variable"
+  echo "$OVERRIDE_BOOTSTRAP_SCRIPT" > /app/bootstrap.sc
+fi
+
 if [ -f /app/bootstrap.sc ]; then
   ARGS+=( --bootstrap /app/bootstrap-entrypoint.sc )
 fi

docs/src/deployment/configuration.rst

@@ -32,11 +32,32 @@ Furthermore, the participant and other synchronizer components can be configured
 
 .. todo:: point to the release that these docs are built from; or inline the source code or Scaladoc to avoid confusion
 
+Custom bootstrap scripts
+++++++++++++++++++++++++
+
+Both Canton and splice support bootstrap scripts during
+initialization. While this usually should not be needed as the
+validator app takes care of initializing the node, in some scenarios
+it can be useful. To do so, you need to set the
+``OVERRIDE_BOOTSTRAP_SCRIPT`` environment variable to the content of your bootstrap script.
+Note that the script must be wrapped in a ``main`` function, e.g.,
+
+.. code::
+
+   def main() {
+     logger.info(s"Participant id from bootstrap script: ${participant.id}")
+   }
+
+You can set this environment variable through ``additionalEnvVars`` as described below.
+
+Note that this overwrites any bootstrap scripts baked into the
+container image. So if you added custom functionality there, you will
+need to replicate this in the overwrite.
 
 Helm charts support
 ^^^^^^^^^^^^^^^^^^^
 
-The helm charts can be configured through the value `additionalEnvVars`, which passes the values as environment variables to the apps.
+The helm charts can be configured through the value ``additionalEnvVars``, which passes the values as environment variables to the apps.
 
 .. code-block:: yaml