# Stage 1: Pull original Alertmanager binary
FROM prom/alertmanager:latest as upstream

# Stage 2: Alpine + envsubst
FROM alpine:latest

# Install envsubst and ca-certificates
RUN apk add --no-cache gettext ca-certificates

# Create directories
RUN mkdir -p /etc/alertmanager /alertmanager

# Copy Alertmanager binary from upstream
COPY --from=upstream /bin/alertmanager /bin/alertmanager
COPY --from=upstream /etc/alertmanager /etc/alertmanager

# Default config will be overwritten by volume mount
ENTRYPOINT ["/bin/sh", "-c"]
CMD ["envsubst < /etc/alertmanager/alertmanager.template.yml > /etc/alertmanager/alertmanager.yml && /bin/alertmanager --config.file=/etc/alertmanager/alertmanager.yml"]