docker: use python for docker-update-hosts

Author: saltydk

roles/docker/files/docker-update-hosts

@@ -0,0 +1,104 @@
+import asyncio
+import subprocess
+import sys
+import tempfile
+
+hosts_file = '/etc/hosts'
+begin_block = "# BEGIN DOCKER CONTAINERS"
+end_block = "# END DOCKER CONTAINERS"
+
+def parse_time_interval(interval_str):
+    """Parse the time interval string into seconds."""
+    units = {'s': 1, 'm': 60, 'h': 3600, 'd': 86400}
+    unit = interval_str[-1]
+    if unit in units:
+        try:
+            value = int(interval_str[:-1])
+            return value * units[unit]
+        except ValueError:
+            raise ValueError("Invalid time interval format.")
+    else:
+        raise ValueError("Unsupported time unit.")
+
+def ensure_managed_section_exists():
+    """Ensures the managed section exists in the hosts file."""
+    with open(hosts_file, 'r+') as file:
+        contents = file.read()
+        # Check if both markers exist
+        if begin_block not in contents or end_block not in contents:
+            print(f"Appending managed section markers to {hosts_file}.", flush = True)
+            # Move to the end of the file before appending
+            file.write(f"\n{begin_block}\n{end_block}\n")
+
+async def update_hosts_file_async():
+    """
+    Asynchronously run the synchronous update_hosts_file function
+    to avoid blocking the asyncio event loop.
+    """
+    loop = asyncio.get_running_loop()
+    await loop.run_in_executor(None, update_hosts_file)
+
+def update_hosts_file():
+    print(f"Updating hosts file", flush = True)
+    
+    # Create a temporary file
+    with tempfile.NamedTemporaryFile(delete=False) as temp_file:
+        hosts_file_tmp = temp_file.name
+    
+    # Build and execute the shell command
+    shell_command = (
+        f"docker container ls -q | xargs -r docker container inspect | "
+        f"jq -r '.[] | if (.NetworkSettings.Networks[].IPAddress | length > 0) then "
+        f"\"\\(.NetworkSettings.Networks[].IPAddress) \\(.NetworkSettings.Networks[].Aliases | select(length > 0) | join(\" \")) "
+        f"\\(.Name | sub(\"^/\"; \"\") | sub(\"_1$\"; \"\") | sub(\"-1$\"; \"\")).saltbox\" else "
+        f"\"# no ip address: \\(.Name | sub(\"^/\"; \"\"))\" end' | "
+        f"sed -ne \"/^{begin_block}$/ {{p; r /dev/stdin\" -e \":a; n; /^{end_block}$/ {{p; b}}; ba}}; p\" {hosts_file} "
+        f"> {hosts_file_tmp}"
+    )
+    
+    subprocess.run(shell_command, shell=True, check=True)
+    
+    # Change file permission
+    subprocess.run(['chmod', '644', hosts_file_tmp], check=True)
+    
+    # Move the temporary file to replace the original hosts file
+    subprocess.run(['mv', hosts_file_tmp, hosts_file], check=True)
+
+async def periodic_update(interval_str):
+    interval_seconds = parse_time_interval(interval_str)
+    while True:
+        # Schedule the synchronous function to run without blocking the asyncio event loop
+        await update_hosts_file_async()
+        await asyncio.sleep(interval_seconds)
+
+async def monitor_docker_events():
+    # Command to filter Docker events for container start and network disconnect
+    cmd = "docker events --filter 'event=start' --filter 'event=disconnect'"
+    # Start the subprocess
+    process = await asyncio.create_subprocess_shell(cmd, stdout=subprocess.PIPE, stderr=subprocess.PIPE)
+
+    print("Monitoring for Docker container start and network disconnect events", flush = True)
+    async for line in process.stdout:
+        print(f"Event received: {line.decode('utf-8').strip()}", flush = True)
+        await update_hosts_file_async()
+
+    # Wait for the process to exit (though in practice, this might run indefinitely)
+    await process.wait()
+
+async def main():
+    # Ensure the managed section exists
+    ensure_managed_section_exists()
+
+    if len(sys.argv) < 2:
+        print("Usage: python script.py <interval>", flush = True)
+        return
+
+    interval_str = sys.argv[1]
+    # Start both the Docker event monitoring and the periodic update tasks
+    await asyncio.gather(
+        monitor_docker_events(),
+        periodic_update(interval_str)
+    )
+
+if __name__ == '__main__':
+    asyncio.run(main())

roles/docker/files/docker-update-hosts.py

@@ -19,21 +19,10 @@
     path: /etc/systemd/system/docker-update-hosts.service
     state: absent
 
-- name: DNS | Import 'docker-update-hosts'
-  ansible.builtin.copy:
-    src: docker-update-hosts
-    force: true
-    dest: "/usr/local/bin/docker-update-hosts"
-    owner: "root"
-    group: "root"
-    mode: "0755"
-
-- name: DNS | Set 'docker-update-hosts' as executable
+- name: DNS | Delete 'docker-update-hosts'
   ansible.builtin.file:
-    path: /usr/local/bin/docker-update-hosts
-    owner: "root"
-    group: "root"
-    mode: a+x
+    path: "/usr/local/bin/docker-update-hosts"
+    state: absent
 
 - name: DNS | Import 'saltbox_managed_docker_update_hosts.service'
   ansible.builtin.template:

roles/docker/tasks/subtasks/dns.yml

@@ -14,7 +14,7 @@ After=docker.service
 PartOf=docker.service
 
 [Service]
-ExecStart=/usr/local/bin/docker-update-hosts {{ docker_update_hosts_service_runtime_max }}
+ExecStart=/usr/bin/python3.10 /srv/git/saltbox/roles/docker/files/docker-update-hosts.py {{ docker_update_hosts_service_runtime_max }}
 Restart=always
 RestartSec=20s
 StartLimitInterval=0