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Mercure

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Mercure is a real-time communication protocol and hub designed for modern web apps. It allows servers to instantly push updates to browsers, mobile clients, and backend workers through Server-Sent Events (SSE).

Built for simplicity and performance, Mercure is widely used in the Symfony ecosystem and beyond for reactive UIs, real-time notifications, and live data streaming.

Supported versions Anchor to this heading

You can select the major version. The latest compatible minor version is applied automatically and can’t be overridden.

Patch versions are applied periodically for bug fixes and the like. When you deploy your app, you always get the latest available patches.

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JWT Token Secret Anchor to this heading

The service generates the JSON Web Token (JWT) token secret. It’s available in the password field of the Mercure relationship in the PLATFORM_RELATIONSHIPS environment variable.

Relationship reference Anchor to this heading

For each service defined via a relationship to your application, Upsun generates corresponding environment variables within your application container, in the $<RELATIONSHIP-NAME>_<SERVICE-PROPERTY> format.

Here is example information available through the service environment variables or through the PLATFORM_RELATIONSHIPS environment variable.

You can obtain the complete list of available service environment variables in your app container by running upsun ssh env.

Relationship information can change when an app is redeployed or restarted, or the relationship is changed. Avoid hard-coding; use the service environment variables to handle dynamic relationship changes.

MERCURE_PUBLIC=false
MERCURE_SERVICE=mercure0
MERCURE_HOSTNAME=sample-hostname.mercure.service.platformsh.site
MERCURE_PORT=3000
MERCURE_IP="123.456.78.90"
MERCURE_CLUSTER=sample-cluster-id-12345
MERCURE_TYPE=mercure:0
MERCURE_QUERY={}
MERCURE_INSTANCE_IPS=["123.456.789.001"]
MERCURE_PATH=
MERCURE_RELATIONSHIPS_ENV_VAR_EXTRA={}
MERCURE_FRAGMENT=
MERCURE_EPOCH=0
MERCURE_HOST=mercure0.internal
MERCURE_PASSWORD=ChangeMe
MERCURE_HOST_MAPPED=false
MERCURE_SCHEME=http
MERCURE_REL=mercure
MERCURE_USERNAME=

For some advanced use cases, you can use the PLATFORM_RELATIONSHIPS environment variable. The structure of the PLATFORM_RELATIONSHIPS environment variable can be obtained by running upsun relationships in your terminal:

{
  "mercure": [
    {
      "username": null,
      "fragment": null,
      "ip": "123.456.78.90",
      "cluster": "sample-cluster-id-12345",
      "host": "mercure.internal",
      "path": null,
      "query": {},
      "relationships_env_var_extra": {},
      "port": 3000,
      "host_mapped": false,
      "password": "ChangeMe",
      "service": "mercure",
      "hostname": "sample-hostname.mercure.service.platformsh.site",
      "epoch": 0,
      "instance_ips": [
        "123.456.789.001"
      ],
      "rel": "mercure",
      "scheme": "http",
      "type": "mercure:0",
      "public": false
    }
  ]
}

Here is an example of how to gather PLATFORM_RELATIONSHIPS environment variable information in a .environment file:

.environment 
# Decode the built-in credentials object variable.
export RELATIONSHIPS_JSON="$(echo "$PLATFORM_RELATIONSHIPS" | base64 --decode)"

# Set environment variables for individual credentials.
export APP_MERCURE_HOST="$(echo $RELATIONSHIPS_JSON | jq -r '.mercure[0].host')"

Usage example Anchor to this heading

1. Configure the service Anchor to this heading

To define the service, use the mercure type:

.upsun/config.yaml 
services:
   # The name of the service container. Must be unique within a project.
   <SERVICE_NAME>:
      type: mercure:0
      disk: 256

Note that changing the name of the service replaces it with a brand new service and all existing data is lost. Back up your data before changing the service.

2. Define the route Anchor to this heading

To access the service URL, add an entry to the .routes key as shown below, replacing <APP_NAME> with the name of your app:

.upsun/config.yaml 
routes: 
  "https://mercure.{default}/":
    type: upstream
    upstream: "<APP_NAME>:mercure"

3. Define the relationship Anchor to this heading

Define the relationship to the app as shown below:

.upsun/config.yaml 
applications:
  # The name of the app container. Must be unique within a project.
  <APP_NAME>:
    # Relationships enable access from this app to a given service.
    # The example below shows simplified configuration leveraging a default service
    # (identified from the relationship name) and a default endpoint.
    # See the Application reference for all options for defining relationships and endpoints.
    relationships:
      <SERVICE_NAME>: "mercure:mercure"

You can define <SERVICE_NAME> as you like, so long as it’s unique between all defined services and matches in both the application and services configuration.

The example above leverages default endpoint configuration for relationships. That is, it uses default endpoints behind the scenes, providing a relationship (the network address a service is accessible from) that is identical to the name of that service.

Depending on your needs, instead of default endpoint configuration, you can use explicit endpoint configuration.

With the above definition, the application container now has access to the service via the relationship <SERVICE_NAME> and its corresponding service environment variables.

.upsun/config.yaml 
applications:
  # The name of the app container. Must be unique within a project.
  <APP_NAME>:
    # Relationships enable access from this app to a given service.
    # The example below shows configuration with an explicitly set service name and endpoint.
    # See the Application reference for all options for defining relationships and endpoints.
    relationships:
      <RELATIONSHIP_NAME>:
        service: <SERVICE_NAME>
        endpoint: mercure

You can define <SERVICE_NAME> and <RELATIONSHIP_NAME> as you like, so long as it’s unique between all defined services and relationships and matches in both the application and services configuration.

The example above leverages explicit endpoint configuration for relationships.

Depending on your needs, instead of explicit endpoint configuration, you can use default endpoint configuration.

With the above definition, the application container now has access to the service via the relationship <RELATIONSHIP_NAME> and its corresponding service environment variables.

Example configuration Anchor to this heading

.upsun/config.yaml 
applications:
  # The name of the app container. Must be unique within a project.
  myapp:
    # Relationships enable access from this app to a given service.
    # The example below shows simplified configuration leveraging a default service
    # (identified from the relationship name) and a default endpoint.
    # See the Application reference for all options for defining relationships and endpoints.
    relationships:
      mercure:

services:
  # The name of the service container. Must be unique within a project.
  mercure:
    type: mercure:0
.upsun/config.yaml 
applications:
  # The name of the app container. Must be unique within a project.
  myapp:
    # Relationships enable access from this app to a given service.
    # The example below shows configuration with an explicitly set service name and endpoint.
    # See the Application reference for all options for defining relationships and endpoints.
    relationships:
      mercure: "mercure:mercure"

services:
  # The name of the service container. Must be unique within a project.
  mercure:
    type: mercure:0

Use in app Anchor to this heading

To use the configured service in your app, add a configuration file similar to the following to your project.

.upsun/config.yaml 
applications:
  # The name of the app container. Must be unique within a project.
  myapp:
    # The location of the application's code.
    source:
      root: "/"

    [...]

    # Relationships enable access from this app to a given service.
    # The example below shows simplified configuration leveraging a default service
    # (identified from the relationship name) and a default endpoint.
    # See the Application reference for all options for defining relationships and endpoints.
    relationships:
      mercure:

services:
  mercure:
    type: mercure:0
.upsun/config.yaml 
applications:
  # The name of the app container. Must be unique within a project.
  myapp:
    # The location of the application's code.
    source:
      root: "myapp"

    [...]

    # Relationships enable access from this app to a given service.
    # The example below shows configuration with an explicitly set service name and endpoint.
    # See the Application reference for all options for defining relationships and endpoints.
    relationships:
      mercure:
        service: mercure
        endpoint: mercure
services:
  mercure:
    type: mercure:0

This configuration defines a single application (myapp), whose source code exists in the <PROJECT_ROOT>/myapp directory.
myapp has access to the mercure service via a relationship whose name is identical to the service name (as per default endpoint configuration for relationships).

From this, myapp can retrieve access credentials to the service through the relationship environment variables.

myapp/.environment 
# Set environment variables for common Mercure credentials.
# For more information, please visit https://docs.upsun.com/development/variables.html#service-environment-variables.
export MERCURE_USER="${MERCURE_USERNAME}"
export MERCURE_HOST="${MERCURE_HOST}"
export MERCURE_QUERY="${$MERCURE_QUERY}"

The .environment shown above in the myapp directory is automatically sourced by Upsun into the runtime environment, so that the variable MERCURE_HOST can be used within the application to connect to the service.

Note that all Upsun service environment variables such as MERCURE_HOST are environment-dependent. Unlike the build produced for a given commit, they can’t be reused across environments and only allow your app to connect to a single service instance on a single environment.

A file very similar to this is generated automatically for your when using the upsun project:init command to migrate a codebase to Upsun.