S2I Compatibility

Applies to: Only when building Source-to-Image (S2I) builder images

What Is S2I

Source-to-Image (S2I) is an OpenShift build strategy that produces ready-to-run images by injecting application source code into a builder image. The builder image provides the runtime environment and scripts to compile/prepare the source.

S2I is an optional pattern. Most modern applications use standard Containerfile builds or Tekton pipelines. S2I is relevant when building platform-managed builder images that accept source from developers.

Required Labels

Label Purpose Example
io.openshift.s2i.scripts-url Location of assemble/run/save-artifacts scripts image:///usr/libexec/s2i
io.openshift.s2i.destination Working directory for S2I operations /tmp (default)
io.openshift.s2i.assemble-user UID to run the assemble script as 1001

Required Scripts

Script Purpose Required?
assemble Build the application from source ✅ Yes
run Start the application ✅ Yes
save-artifacts Save build artifacts for incremental builds Optional
usage Print usage instructions Optional

S2I Builder Image Example

FROM registry.access.redhat.com/ubi9/ubi-minimal:latest

LABEL name="mycompany/nodejs-builder" \
      vendor="My Company" \
      version="1.0.0" \
      release="1" \
      summary="Node.js S2I Builder" \
      description="S2I builder for Node.js applications" \
      io.openshift.tags="builder,nodejs" \
      io.openshift.s2i.scripts-url="image:///usr/libexec/s2i" \
      io.k8s.display-name="Node.js Builder" \
      io.k8s.description="S2I builder for Node.js applications"

RUN microdnf install -y nodejs npm && \
    microdnf clean all

# S2I scripts
COPY s2i/bin/ /usr/libexec/s2i/

# Source destination
RUN mkdir -p /opt/app-root/src && \
    chgrp -R 0 /opt/app-root && \
    chmod -R g=u /opt/app-root

# License
COPY LICENSE /licenses/LICENSE

USER 1001
WORKDIR /opt/app-root/src
EXPOSE 8080

CMD ["/usr/libexec/s2i/usage"]

assemble script

#!/bin/bash
# /usr/libexec/s2i/assemble
set -e

echo "---> Installing application source..."
cp -Rf /tmp/src/. ./

if [ -f package.json ]; then
    echo "---> Installing dependencies..."
    npm ci --production
fi

run script

#!/bin/bash
# /usr/libexec/s2i/run
exec node ${APP_SCRIPT:-server.js}

S2I Script Lookup Order

When building, S2I checks for scripts in this order:

  1. Scripts specified in the BuildConfig scripts field
  2. Scripts in the application source .s2i/bin/ directory
  3. Scripts at the URL specified by io.openshift.s2i.scripts-url
  4. Scripts at the default /usr/libexec/s2i/ path

Gotchas

Sources