[AppService] az webapp log startup: Add commands to list and view Linux container startup logs

src/azure-cli/azure/cli/command_modules/appservice/_help.py

@@ -2365,6 +2365,39 @@
     text: az webapp log deployment list --name MyWebApp --resource-group MyResourceGroup
 """
 
+helps['webapp log startup'] = """
+type: group
+short-summary: View web app container startup logs.
+long-summary: >
+    View startup logs written during container initialization for Linux web apps.
+    Use when a container fails to start, crashes on cold start, times out waiting
+    for a port, or returns HTTP 502/503 errors after deployment. These logs contain
+    platform lifecycle events and container stdout/stderr output.
+"""
+
+helps['webapp log startup list'] = """
+type: command
+short-summary: List all container startup log files for a web app.
+examples:
+  - name: List all startup log files
+    text: az webapp log startup list --name MyWebApp --resource-group MyResourceGroup
+  - name: List only failure logs
+    text: az webapp log startup list --name MyWebApp --resource-group MyResourceGroup --outcome failure
+"""
+
+helps['webapp log startup show'] = """
+type: command
+short-summary: Show the content of a container startup log.
+long-summary: By default, shows the most recent startup log, preferring failure logs. Use --filename to view a specific log file, or --instance to scope to a specific worker.
+examples:
+  - name: Show the latest startup log (prefers failures)
+    text: az webapp log startup show --name MyWebApp --resource-group MyResourceGroup
+  - name: Show a specific startup log file
+    text: az webapp log startup show --name MyWebApp --resource-group MyResourceGroup --filename 2026_04_13_lw0sdlwk000002_failure.log
+  - name: Show the latest startup log for a specific worker instance
+    text: az webapp log startup show --name MyWebApp --resource-group MyResourceGroup --instance lw0sdlwk000002
+"""
+
 helps['functionapp log'] = """
 type: group
 short-summary: Manage function app logs.

src/azure-cli/azure/cli/command_modules/appservice/_params.py

@@ -780,6 +780,19 @@ def load_arguments(self, _):
         c.argument('resource_group', arg_type=resource_group_name_type)
         c.argument('slot', options_list=['--slot', '-s'], help="the name of the slot. Default to the productions slot if not specified")
 
+    with self.argument_context('webapp log startup') as c:
+        c.argument('name', arg_type=webapp_name_arg_type, id_part=None)
+        c.argument('resource_group', arg_type=resource_group_name_type)
+        c.argument('slot', options_list=['--slot', '-s'], help="the name of the slot. Default to the production slot if not specified")
+        c.argument('instance', options_list=['--instance'], help='Filter by worker instance name.')
+
+    with self.argument_context('webapp log startup list') as c:
+        c.argument('outcome', options_list=['--outcome'], help='Filter by startup outcome.',
+                   arg_type=get_enum_type(['success', 'failure']))
+
+    with self.argument_context('webapp log startup show') as c:
+        c.argument('filename', options_list=['--filename', '-f'], help='Name of a specific startup log file to display. If not specified, shows the latest log (preferring failures).')
+
     with self.argument_context('functionapp log deployment show') as c:
         c.argument('name', arg_type=functionapp_name_arg_type, id_part=None)
         c.argument('resource_group', arg_type=resource_group_name_type)

src/azure-cli/azure/cli/command_modules/appservice/commands.py

@@ -246,6 +246,10 @@ def load_command_table(self, _):
         g.custom_show_command('show', 'show_deployment_log')
         g.custom_command('list', 'list_deployment_logs')
 
+    with self.command_group('webapp log startup', is_preview=True) as g:
+        g.custom_command('list', 'list_startup_logs')
+        g.custom_show_command('show', 'show_startup_log')
+
     with self.command_group('functionapp log deployment') as g:
         g.custom_show_command('show', 'show_deployment_log')
         g.custom_command('list', 'list_deployment_logs')

src/azure-cli/azure/cli/command_modules/appservice/custom.py

@@ -5597,6 +5597,78 @@ def list_deployment_logs(cmd, resource_group, name, slot=None):
     return response.json() or []
 
 
+def list_startup_logs(cmd, resource_group, name, slot=None, outcome=None, instance=None):
+    import requests
+
+    scm_url = _get_scm_url(cmd, resource_group, name, slot)
+    headers = get_scm_site_headers(cmd.cli_ctx, name, resource_group, slot)
+
+    params = {}
+    if outcome:
+        params['type'] = outcome
+    if instance:
+        params['instance'] = instance
+
+    url = '{}/api/startuplogs'.format(scm_url)
+    response = requests.get(url, headers=headers, params=params)
+
+    if response.status_code == 404:
+        logger.warning(
+            'Startup logs are not available for this app. '
+            'This feature requires a platform version that may not have rolled out to your app\'s region yet.')
+        return []
+    if response.status_code != 200:
+        raise CLIError("Failed to retrieve startup logs from '{}' with status code '{}' and reason '{}'".format(
+            url, response.status_code, response.reason))
+
+    result = response.json()
+    return result.get('files', result) if isinstance(result, dict) else result
+
+
+def show_startup_log(cmd, resource_group, name, slot=None, filename=None, instance=None):
+    import requests
+
+    scm_url = _get_scm_url(cmd, resource_group, name, slot)
+    headers = get_scm_site_headers(cmd.cli_ctx, name, resource_group, slot)
+
+    if filename:
+        url = '{}/api/startuplogs/{}'.format(scm_url, quote(filename, safe=''))
+    else:
+        url = '{}/api/startuplogs?latest=true'.format(scm_url)
+        if instance:
+            url += '&instance={}'.format(quote(instance, safe=''))
+
+    response = requests.get(url, headers=headers)
+
+    if response.status_code == 404:
+        if filename:
+            logger.warning('Startup log file \'%s\' was not found.', filename)
+        else:
+            logger.warning(
+                'Startup logs are not available for this app. '
+                'This feature requires a platform version that may not have rolled out to your app\'s region yet.')
+        return None
+    if response.status_code != 200:
+        raise CLIError("Failed to retrieve startup log from '{}' with status code '{}' and reason '{}'".format(
+            url, response.status_code, response.reason))
+
+    content_type = response.headers.get('Content-Type', '')
+    if 'text/plain' in content_type:
+        # Raw log content — return metadata from headers along with content
+        log_content = response.text
+        metadata = {}
+        for header_name in ['X-StartupLog-Filename', 'X-StartupLog-Date', 'X-StartupLog-Instance',
+                            'X-StartupLog-Outcome']:
+            value = response.headers.get(header_name)
+            if value:
+                key = header_name.replace('X-StartupLog-', '').lower()
+                metadata[key] = value
+        metadata['content'] = log_content
+        return metadata
+
+    return response.json()
+
+
 def config_slot_auto_swap(cmd, resource_group_name, webapp, slot, auto_swap_slot=None, disable=None):
     client = web_client_factory(cmd.cli_ctx)
     site_config = client.web_apps.get_configuration_slot(resource_group_name, webapp, slot)
@@ -8521,6 +8593,11 @@ def _poll_deployment_runtime_status(cmd, resource_group_name, webapp_name, slot,
             if failure_logs is not None and len(failure_logs) > 0:
                 failure_logs = failure_logs[0]
             error_text += "Please check the runtime logs for more info: {}\n".format(failure_logs)
+            tip_cmd = "az webapp log startup show -n {} -g {}".format(webapp_name, resource_group_name)
+            if slot:
+                tip_cmd += " --slot {}".format(slot)
+            error_text += ("TIP: Run '{}' "
+                           "to view container startup logs.\n").format(tip_cmd)
             if site_started_partially:
                 logger.warning(error_text)
                 break
@@ -8565,6 +8642,11 @@ def _poll_deployment_runtime_status(cmd, resource_group_name, webapp_name, slot,
                           deployment_properties.get('numberOfInstancesInProgress'),
                           deployment_properties.get('numberOfInstancesSuccessful'),
                           deployment_properties.get('numberOfInstancesFailed'))
+        tip_cmd = "az webapp log startup show -n {} -g {}".format(webapp_name, resource_group_name)
+        if slot:
+            tip_cmd += " --slot {}".format(slot)
+        error_text += ("\nTIP: Run '{}' "
+                       "to view container startup logs.").format(tip_cmd)
         raise CLIError(error_text)
     return response_body