Shell scripting for DevOps automation

#!/bin/bash
set -euo pipefail

# Colors for output
RED='\033[0;31m'
GREEN='\033[0;32m'
YELLOW='\033[1;33m'
BLUE='\033[0;34m'
NC='\033[0m' # No Color

# Logging functions
log()   { echo -e "${BLUE}[$(date +'%Y-%m-%d %H:%M:%S')]${NC} $*"; }
info()  { echo -e "${GREEN}[INFO]${NC} $*"; }
warn()  { echo -e "${YELLOW}[WARN]${NC} $*"; }
error() { echo -e "${RED}[ERROR]${NC} $*" >&2; }

# Configuration
APP_NAME="${APP_NAME:-web-app}"
ENVIRONMENT="${ENVIRONMENT:-staging}"
IMAGE_TAG="${IMAGE_TAG:-latest}"
NAMESPACE="${NAMESPACE:-$ENVIRONMENT}"
TIMEOUT="${TIMEOUT:-300}"
HEALTH_URL="${HEALTH_URL:-https://$ENVIRONMENT.example.com/health}"

# Parse arguments
usage() {
  cat <<EOF
Usage: $(basename "$0") [OPTIONS]

Deploy application to Kubernetes

Options:
  -e, --environment   Target environment (default: staging)
  -t, --tag           Docker image tag (default: latest)
  -n, --namespace     Kubernetes namespace
  -d, --dry-run       Show what would be done
  -h, --help          Show this help
EOF
}

DRY_RUN=false

while [[ $# -gt 0 ]]; do
  case "$1" in
    -e|--environment) ENVIRONMENT="$2"; shift 2 ;;
    -t|--tag)         IMAGE_TAG="$2"; shift 2 ;;
    -n|--namespace)   NAMESPACE="$2"; shift 2 ;;
    -d|--dry-run)     DRY_RUN=true; shift ;;
    -h|--help)        usage; exit 0 ;;
    *)                error "Unknown option: $1"; usage; exit 1 ;;
  esac
done

# Cleanup on exit
TMPDIR=$(mktemp -d)
trap 'rm -rf "$TMPDIR"' EXIT

# Pre-flight checks
preflight() {
  log "Running pre-flight checks..."

  command -v kubectl >/dev/null 2>&1 || { error "kubectl not found"; exit 1; }
  command -v jq >/dev/null 2>&1 || { error "jq not found"; exit 1; }

  # Check cluster connection
  if ! kubectl cluster-info &>/dev/null; then
    error "Cannot connect to Kubernetes cluster"
    exit 1
  fi

  # Check namespace exists
  if ! kubectl get namespace "$NAMESPACE" &>/dev/null; then
    error "Namespace $NAMESPACE does not exist"
    exit 1
  fi

  # Check image exists
  if ! docker manifest inspect "registry.example.com/$APP_NAME:$IMAGE_TAG" &>/dev/null; then
    error "Image $APP_NAME:$IMAGE_TAG not found in registry"
    exit 1
  fi

  info "Pre-flight checks passed"
}

# Deploy
deploy() {
  log "Deploying $APP_NAME:$IMAGE_TAG to $ENVIRONMENT..."

  if [[ "$DRY_RUN" == true ]]; then
    warn "DRY RUN - no changes will be made"
    kubectl set image "deployment/$APP_NAME"       "$APP_NAME=registry.example.com/$APP_NAME:$IMAGE_TAG"       -n "$NAMESPACE" --dry-run=client
    return
  fi

  # Record current revision for rollback
  CURRENT_REV=$(kubectl rollout history "deployment/$APP_NAME"     -n "$NAMESPACE" -o json | jq '.metadata.generation')
  info "Current revision: $CURRENT_REV"

  # Update image
  kubectl set image "deployment/$APP_NAME"     "$APP_NAME=registry.example.com/$APP_NAME:$IMAGE_TAG"     -n "$NAMESPACE"

  kubectl annotate "deployment/$APP_NAME"     "kubernetes.io/change-cause=Deploy $IMAGE_TAG via deploy.sh"     -n "$NAMESPACE" --overwrite

  info "Image updated, waiting for rollout..."
}

# Wait for rollout
wait_for_rollout() {
  if [[ "$DRY_RUN" == true ]]; then return; fi

  if ! kubectl rollout status "deployment/$APP_NAME"     -n "$NAMESPACE" --timeout="${TIMEOUT}s"; then
    error "Rollout failed! Rolling back..."
    kubectl rollout undo "deployment/$APP_NAME" -n "$NAMESPACE"
    kubectl rollout status "deployment/$APP_NAME"       -n "$NAMESPACE" --timeout="${TIMEOUT}s"
    error "Rolled back to previous version"
    exit 1
  fi

  info "Rollout completed successfully"
}

# Health check
health_check() {
  if [[ "$DRY_RUN" == true ]]; then return; fi

  log "Running health checks..."
  local retries=10
  local delay=5

  for ((i=1; i<=retries; i++)); do
    HTTP_CODE=$(curl -s -o /dev/null -w '%{http_code}' "$HEALTH_URL" || true)

    if [[ "$HTTP_CODE" == "200" ]]; then
      info "Health check passed (HTTP $HTTP_CODE)"
      return 0
    fi

    warn "Attempt $i/$retries: HTTP $HTTP_CODE (retrying in ${delay}s)"
    sleep "$delay"
  done

  error "Health check failed after $retries attempts"
  return 1
}

# Main
main() {
  log "=== Deployment: $APP_NAME → $ENVIRONMENT ==="
  preflight
  deploy
  wait_for_rollout
  health_check
  info "=== Deployment complete! ==="
}

main