Replace certbot cron with systemd timer.

.ebextensions/21-certbot.config

@@ -36,9 +36,35 @@
 #       # Reload the nginx configuration every time, since there may be multiple servers running. Using --renew-hook would only reload nginx on the server that made the renewal.
 #       systemctl reload nginx.service
 #
-#   /etc/cron.d/certbot:
+#   /etc/systemd/system/certbot-renew.service:
 #     mode: "000644"
 #     owner: root
 #     group: root
 #     content: |
-#       @daily root /opt/certbot-renew
+#       [Unit]
+#       Description="Service that runs /opt/certbot-renew"
+#       Requires=certbot-renew.timer
+#       [Service]
+#       Type=simple
+#       ExecStart=/opt/certbot-renew
+#
+#   /etc/systemd/system/certbot-renew.timer:
+#     mode: "000644"
+#     owner: root
+#     group: root
+#     content: |
+#       [Unit]
+#       Description="Timer for certbot-renew.service"
+#       [Timer]
+#       Unit=certbot-renew.service
+#       OnBootSec=5m
+#       OnUnitActiveSec=1d
+#       [Install]
+#       WantedBy=timers.target
+#
+# container_commands:
+#   "01-enable-timer":
+#     command: |
+#       systemctl daemon-reload
+#       systemctl enable certbot-renew.timer
+#       systemctl start certbot-renew.timer