Remote execution support in Pants comes with several limitations. For example, Pants requires that the server's operating system match the client's operating system. In practice, this means that Pants must be running on Linux because all three major server projects generally only operate on Linux.
What is remote execution?
"Remote execution" allows Pants to offload execution of processes to a remote server that complies with the Remote Execution API standard ("REAPI"). The REAPI standard is supported by several different server and client projects including Bazel and of course Pants.
Setup
Server
Remote execution requires the availability of a REAPI-compatible execution server. See the REAPI server compatibility guide for more information.
Pants
After you have either set up a REAPI server or obtained access to one, the next step is to point Pants to it so that Pants may submit REAPI execution requests. The server should be running a CAS and execution service. These may be the same network endpoint, but for Pants' purposes, they are configured by different configuration options.
For the following examples, assume that the REAPI server is running on build.corp.example.com at port 8980 and that it is on an internal network (and for the sake of this example is not running TLS, which will be covered later). Also, assume that the name of the REAPI instance is "main." At a minimum, you will need to configure pants.toml as follows:
[GLOBAL]
remote_execution = true
remote_store_address = "grpc://build.corp.example.com:8980"
remote_execution_address = "grpc://build.corp.example.com:8980"
remote_instance_name = "main"
Environment-specific settings
The REAPI execution service selects a worker for a process by consulting the "platform properties" that are passed in a remote execution request. These platform properties are key/value pairs that are configured for particular workers in the server. Generally, you will configure these in the server (or be provided them by your server's administrator), and then configure Pants to match particular workers using their relevant platform properties.
To define platform properties (as well as to configure any other settings which are specific to running on a remote worker), you should define a remote environment. Building on the first example earlier, you would add remote_environment targets (see environment for more information) corresponding to each set of distinct workers you want to use in the server. Assuming that the REAPI server is configured with a particular worker type labeled docker-container=busybox:latest, that might look like a BUILD file containing:
remote_environment(
name="remote_busybox",
platform="linux_x86_64",
extra_platform_properties = [
"docker-container=busybox:latest",
],
..
)
Your remote_environment will also need to override any environment-aware options which configure the relevant tools used in your repository. For example: if building Python code, a Python interpreter must be available and matched via the environment-aware options of [python-bootstrap]. If using protobuf support, then you may also need unzip available in the remote execution environment in order to unpack the protoc archive. Etc.
Concurrency
Finally, you should configure Pants to limit the number of concurrent execution requests that are sent to the REAPI server. The process_execution_remote_parallelism option controls this concurrency. For example, if process_execution_remote_parallelism is set to 20, then Pants will only send a maximum of 20 execution requests at a single moment of time.
Note: The specific value depends on the resources available to the REAPI server. If this value is configured to a high number, then Pants will happily send that many concurrent execution requests, which could potentially overwhelm the REAPI server.
Building on the previous example, pants.toml would contain:
[GLOBAL]
remote_execution = true
remote_store_address = "grpc://build.corp.example.com:8980"
remote_execution_address = "grpc://build.corp.example.com:8980"
remote_instance_name = "main"
remote_execution_extra_platform_properties = [
"OSFamily=linux",
]
process_execution_remote_parallelism = 20
TLS
You can enable TLS by prefixing the remote_store_address and remote_execution_address with grpcs:// instead of grpc://.
Pants will automatically discover root CA certificates on your machine, but you can also configure Pants to use your preferred certificates with the --remote-ca-certs-path option.
Assume that the REAPI server is running on port 443 (https/TLS) at build.example.com. Then the relevant parts of pants.toml would contain:
[GLOBAL]
remote_execution = true
remote_store_address = "grpcs://build.example.com:443"
remote_execution_address = "grpcs://build.example.com:443"
remote_instance_name = "main"
# This is optional, Pants will auto-discover certificates otherwise.
remote_ca_certs_path = "/etc/ssl/certs/ca-certificates.crt"
Reference
For global options, run pants help-advanced global or refer to Global options. Most remote execution and caching options begin with the prefix --remote.
For environment-specific options, see pants help-advanced remote_environment or the remote_environment target.