service: use --no-el flag when no exec URLs set

Signed-off-by: Jakub Sokołowski <jakub@status.im>

tasks/checks.yml

@@ -1,12 +1,4 @@
 ---
-- name: Verify Exec layer Engine API URLs are provided
-  assert:
-    that: '{{ beacon_node_exec_layer_urls|length > 0 }}'
-    quiet: true
-    fail_msg: |
-      Providing Exec layer Engine API URLs is required to sync with Eth1 chain!
-      Verify that the 'beacon_node_exec_layer_urls' variable is set.
-
 - name: Verify network name
   assert:
     that: '{{ beacon_node_network in beacon_node_valid_network_names }}'

tasks/service.yml

@@ -21,9 +21,13 @@
       --validators-dir="{{ beacon_node_validators_path }}"
       --era-dir="{{ beacon_node_era_dir_path }}"
       --history="{{ beacon_node_history_retention }}"
+      {% if beacon_node_exec_layer_urls|length == 0 %}
+      --no-el=true
+      {% else %}
       {% for url in beacon_node_exec_layer_urls | mandatory %}
       --el="{{ url | mandatory }}"
       {% endfor %}
+      {% endif %}
       {% if beacon_node_exec_layer_jwt_secret is defined %}
       --jwt-secret="{{ beacon_node_exec_layer_jwt_secret_path | mandatory }}"
       {% endif %}