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This article mainly explains "how Cloud Foundry BOSH works when deploying the system". The content in the article is simple and clear, and it is easy to learn and understand. Please follow the editor's train of thought to study and learn "how Cloud Foundry BOSH works when deploying the system".

Introduction to Cloud Foundry BOSH

Cloud Foundry is the industry's first open source PaaS, which supports multiple development frameworks, multiple services, and multiple IaaS. BOSH was originally developed in the Cloud Foundry project, but it is a general tool to assist in the deployment and lifecycle management of large-scale distributed services.

We use BOSH to deploy the components of Cloud Foundry to distributed nodes (in a virtualized environment, nodes are virtual machines). The following is a brief description of how BOSH works when deploying the system.

BOSH is the abbreviation of Bosh Outter SHell. As opposed to "Outter Shell", the system deployed and managed by BOSH is called "Inner Shell". The following figure briefly illustrates the module of BOSH:

BOSH is a server that defines and orchestrates the deployment steps of a distributed system. It can interact with the BOSH server through BOSH CLI (instruction interface, a ruby tool). Before BOSH can start deploying the system, there are three things to prepare: stemcell,release (the software to be installed), and a deployment manifest (manifest). Let's take a closer look at these three items:

Stemcells: on cloud platforms, VM is often created by clone from a template. Stemcell is a VM template that contains standard operating systems such as ubuntu and BOSH agent. The word "stemcell" comes from the biological "stem cell", which refers to primordial cells that can grow into different types of cells. The same VM created by BOSH stemcell is the same at the beginning, and after startup, VM is configured as a different CPU/memory/storage/network and different packages are installed. This makes the VM created from the same stemcell template different.

Releases: release contains a range of software and configurations for installation to the target system. Configuration usually includes, for example, IP address, trade number, user name, password, domain name, and so on. These parameters are determined based on the properties in the deployment manifest file (Deployment mManifest).

Contains collections of software bits and configurations which will be installed onto the target system. Each VM is deployed with a collection of software, which is called a job. Configurations are usually templates which contain parameters such as IP address, port number, user name, password, domain name. These parameters will be replaced at deploy time by the properties defined in a deployment manifest file.

Deployment Manifest: Deployment Manifest (deployment manifest) defines the actual parameter values required for deployment, and during deployment, BOSH replaces the parameters in release with these values so that the software runs as planned.

When the above three items are ready, they will be uploaded to BOSH using the BOSH CLI tool. Then, installing a distributed system with BOSH generally includes the following host steps:

1) if some package in release needs to be compiled, BOSH first creates several temporary VM to compile them. When the compilation is complete, BOSH places the compiled binaries in the internal blobstore and destroys the temporary VM.

2) BOSH creates a VM pool that contains multiple VM,release to be deployed on these VM. These VM have been cloned from stemcell, and they already contain BOSH agent.

3) when deploying a release task, BOSH takes a VM from the VM pool and changes the configuration according to Deployment Manifest. Configuration may include IP address, permanent disk size, and so on.

4) when the reconfiguration of VM is complete, BOSH sends instructions to the agent in each VM. These instructions tell agent to install the package. During installation, agent may download the package from BOSH and install it. When the installation is complete, agent runs the startup script to start the task in VM.

5) BOSH repeat steps 3-4 until all tasks have been deployed and started. These tasks can be deployed in parallel or sequentially, controlled by the "max_in_flight" value in the manifest (manifest) file. When set to 1, the tasks are deployed one by one. This value is useful for systems with poor performance to avoid timeouts caused by resource congestion. When this value is greater than 1, it means that the task can be deployed in parallel.

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