1. Deployment Environment: One key difference between Apollo and Heroku is the deployment environment. Apollo is an open-source GraphQL server that can be self-hosted on any infrastructure, giving users complete control over the deployment process. On the other hand, Heroku is a cloud-based platform as a service (PaaS) that simplifies deployment by providing a fully managed environment for deploying web applications and services.

2. Scalability Options: Another important difference is the scalability options offered by Apollo and Heroku. Apollo allows users to scale their GraphQL server horizontally by adding more instances as needed, giving them flexibility in handling increased traffic and workload. Heroku, on the other hand, automatically handles scaling based on the application's needs, making it easier for users to manage resources without having to intervene manually.

3. Cost Structure: The cost structure differs between Apollo and Heroku. Apollo being open-source, has no direct cost associated with using the software itself, but users are responsible for the infrastructure and maintenance costs if self-hosted. In contrast, Heroku offers a pay-as-you-go model, where users only pay for the resources and services they use, making it a more convenient option for those who prefer a simple pricing structure.

4. Add-on Services: Heroku provides a wide range of add-on services that can be easily integrated into applications, such as databases, caching, logging, monitoring, and more. These add-ons help enhance the functionality and performance of applications deployed on Heroku. Apollo, being a server framework, does not offer similar add-on services but can be integrated with various third-party services to supplement its capabilities.

5. Community Support and Ecosystem: When it comes to community support and ecosystem, Apollo benefits from a large, active community contributing to its development and providing resources such as tutorials, libraries, and plugins. Heroku, being a popular PaaS platform, has a vast ecosystem of developers, partners, and integrations, making it easier for users to find solutions and resources to support their applications.

6. Integration Flexibility: Lastly, the integration flexibility differs between Apollo and Heroku. Apollo, being a self-hosted server, offers users more control and flexibility in integrating with other tools, services, and platforms as needed. Heroku, while providing seamless integration with its own ecosystem of add-ons, may have limitations when it comes to integrating with certain external services, requiring users to find workarounds or alternative solutions.

In Summary, the key differences between Apollo and Heroku lie in the deployment environment, scalability options, cost structure, add-on services, community support, and integration flexibility.