To connect PHP to a managed MQTT broker, install the php-mqtt/client library, use the endpoint and credentials supplied by your broker deployment, configure TLS, then connect and run the client loop to receive messages and process acknowledgements. This guide uses EMQX Cloud Serverless as its concrete example; its hostname, username, password, and CA certificate must come from your own deployment.
What you need to connect
An MQTT connection has five pieces: a PHP application, an MQTT client library, a broker endpoint, a client identity, and one or more topic names. The library handles the MQTT protocol; the broker routes messages between clients that publish to or subscribe to matching topics.
- Broker endpoint: the deployment’s hostname and supported port.
- Client identity: a client ID that is unique among clients connected to that deployment.
- Authentication and transport: credentials and TLS settings required by the broker.
- Topics and payloads: the topic strings your application uses to publish and subscribe.
Do not substitute generic values for a provider’s endpoint settings. Managed brokers can differ in hostname, authentication method, certificate authority, ports, and protocol support.
Install the PHP MQTT client
From your PHP project directory, install the library with Composer:
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composer require php-mqtt/clientThe php-mqtt/client documentation describes its API for connecting, publishing, subscribing, and processing messages. EMQ’s walkthrough uses MQTT 3.1.1 with this library.
Get the connection details from EMQX Cloud
Create or select an EMQX Cloud Serverless deployment and copy its actual connection hostname. Configure username-and-password authentication for that deployment and save the credentials securely. EMQX’s current deployment connection instructions specify TLS for Serverless connections, port 8883, and a CA certificate downloaded for the deployment.
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Use the downloaded CA certificate to verify the broker’s TLS certificate. Do not disable certificate validation as a shortcut: a connection without proper verification does not provide the intended protection against an impersonated endpoint.
Connect, subscribe, and publish
The following illustrates the shape of a PHP client using deployment-specific values. The hostname, credentials, CA path, and topic are examples or environment-provided settings—not working credentials. Replace them with values for your own deployment.
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<?php
require __DIR__ . '/vendor/autoload.php';
use PhpMqttClientMqttClient;
use PhpMqttClientConnectionSettings;
$host = getenv('MQTT_HOST');
$username = getenv('MQTT_USERNAME');
$password = getenv('MQTT_PASSWORD');
$caFile = getenv('MQTT_CA_FILE');
$clientId = getenv('MQTT_CLIENT_ID');
if (!$host || !$username || !$password || !$caFile || !$clientId) {
throw new RuntimeException('Set the MQTT deployment settings before connecting.');
}
$client = new MqttClient($host, 8883, $clientId);
$settings = (new ConnectionSettings())
->setUsername($username)
->setPassword($password)
->setKeepAliveInterval(60)
->setConnectTimeout(10)
->setUseTls(true)
->setTlsVerifyPeer(true)
->setTlsCertificateAuthorityFile($caFile);
$client->connect($settings, true);
$client->subscribe('devices/example/status', function (string $topic, string $message) {
echo "Received on {$topic}: {$message}" . PHP_EOL;
}, 1);
$client->publish('devices/example/status', json_encode([
'state' => 'online',
'sent_at' => gmdate(DATE_ATOM),
]), 1);
// Keep processing incoming packets and QoS acknowledgements.
$client->loop(true);
Use the exact TLS configuration supported by your installed library version and the CA file supplied for your deployment. EMQ’s PHP walkthrough shows how its connection settings carry authentication, keepalive, timeout, and TLS options before connect(); the example values must be replaced with your deployment’s details.
Why the loop matters
A subscription callback is invoked when the client processes a broker message; subscribing alone does not continuously read messages from the network. The library documentation explains that the client loop reads and handles broker packets. It also processes QoS 1 and QoS 2 publication acknowledgements, so a workflow that publishes at those levels must continue running the loop long enough to process them.
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Choose a client ID deliberately
Use a stable, unique ID strategy appropriate to the application, such as a persistent identifier per device or a distinct identifier for each worker. Avoid assigning the same ID to concurrent clients: MQTT brokers commonly treat a new connection using an existing client ID as a replacement for the earlier connection.
Make the connection safe and operational
- Keep secrets out of source control. Supply the username and password through environment variables or a secrets manager, and restrict access to them.
- Verify the broker certificate. Use the deployment’s CA certificate and the provider’s supported verification settings. Do not copy permissive self-signed-certificate settings from a sample without confirming they are appropriate for your actual certificate chain.
- Match process lifetime to the job. A subscriber needs a process that stays alive and runs the MQTT loop. A short-lived PHP web request may end before messages arrive; use a long-running worker or another suitable process manager for continuous subscriptions.
- Handle reconnects and shutdowns. Production workers should detect connection failures, reconnect using the deployment’s current settings, and close connections cleanly when stopping.
EMQX Serverless and AWS IoT Core are not interchangeable
The PHP MQTT library provides a general MQTT client API, but the transport and authentication setup depends on the broker. EMQX Cloud Serverless documents TLS on port 8883, a deployment CA certificate, and deployment-configured username/password authentication. AWS IoT Core has separate endpoint, authentication, and protocol requirements.
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| Connection consideration | EMQX Cloud Serverless | AWS IoT Core |
|---|---|---|
| Transport and endpoint | TLS is required; the documented TLS port is 8883. Use the hostname and CA certificate for your deployment, per EMQX’s instructions. |
Supports MQTT and MQTT over secure WebSockets. Protocols, ports, authentication, and ALPN requirements vary; follow the AWS protocol and port documentation. |
| Authentication and security | Configure deployment username/password authentication and TLS using the deployment’s certificate details. | Authentication depends on the chosen protocol and port. AWS says custom non-SDK clients must meet its security requirements, including sending SNI; connections without SNI are refused. See AWS IoT Core MQTT documentation. |
| Client guidance | A general MQTT client such as php-mqtt/client can be configured with the deployment’s connection settings. |
AWS recommends its Device SDKs. A generic PHP client requires deliberate configuration for AWS’s endpoint security and authentication rules. |
| QoS support | Use the QoS levels supported by your selected deployment and client configuration. | AWS IoT supports QoS 0 and 1, not QoS 2. Wait for CONNACK before sending additional control packets or disconnecting, as described in the AWS MQTT guidance. |
For AWS IoT, select a supported authentication-and-port combination from its protocol documentation rather than assuming EMQX’s TLS settings will work unchanged.
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