A non-interactive daemon for host management
flowchart LR;
subgraph sanssh ["sansshell client (sanssh)"]
cli;
client;
subgraph client modules
package([package]);
file([file]);
exec([exec]);
end
cli --> package --> client;
cli --> file --> client;
cli --> exec --> client;
end
subgraph proxy ["proxy (optional)"]
proxy_server[proxy-server];
opa_policy[(opa policy)];
proxy_server --> opa_policy --> proxy_server
end
subgraph sansshell server ["sansshell server (on each host)"]
server[sansshell-server];
host_apis;
s_opa_policy[(opa policy)];
subgraph service modules
s_package([package]);
s_file([file]);
s_exec([exec]);
end
server --> s_package --> host_apis;
server --> s_file --> host_apis;
server --> s_exec --> host_apis;
server --> s_opa_policy --> server
end
user{user};
user --> cli;
client --"gRPC (mTLS)"--> proxy_server
proxy_server --"grpc (mTLS)"---> server
SansShell is primarily a gRPC server with a variety of options for localhost debugging and management. Its goal is to replace the need to use an interactive shell for emergency debugging and recovery with a much safer interface. Each authorized action can be evaluated against an OPA policy, audited in advance or after the fact, and is ideally deterministic (for a given state of the local machine).
sanssh is a simple CLI with a friendly API for dumping debugging state and interacting with a remote machine. It also includes a set of convenient but perhaps-less-friendly subcommands to address the raw SansShell API endpoints.
How to set up, build and run locally for testing. All commands are relative to the project root directory.
Building SansShell requires a recent version of Go (check the go.mod file for the current version).
You need to populate ~/.sansshell with certificates before running.
$ cp -r auth/mtls/testdata ~/.sansshell
Then you can build and run the server, in separate terminal windows:
$ go run ./cmd/sansshell-server
$ go run ./cmd/sanssh --targets=localhost file read /etc/hosts
You can also run the proxy to try the full flow:
$ go run ./cmd/sansshell-server
$ go run ./cmd/proxy-server
$ go run ./cmd/sanssh --proxy=localhost:50043 --targets=localhost:50042 file read /etc/hosts
Minimal debugging UIs are available at http://localhost:50044 for the server and http://localhost:50046 for the proxy by default.
When making any change to the protocol buffers, you'll also need the protocol
buffer compiler (protoc
) (version 3 or above) as well as the protoc plugins
for Go and Go-GRPC
On MacOS, the protocol buffer can be installed via homebrew using
brew install protobuf
On Linux, protoc can be installed using either the OS package manager, or by directly installing a release version from the protocol buffers github
On any platform, once protoc has been installed, you can install the required
code generation plugins using go install
.
$ go install google.golang.org/protobuf/cmd/protoc-gen-go
$ go install google.golang.org/grpc/cmd/protoc-gen-go-grpc
$ go install github.com/Snowflake-Labs/sansshell/proxy/protoc-gen-go-grpcproxy
Note that, you'll need to make certain that your PATH
includes the gobinary
directory (either the value of $GOBIN
, or, if unset, $HOME/go/bin
)
The tools.go
file contains helpful go generate
directives which will
do this for you, as well as re-generating the service proto files.
$ go generate tools.go
Configuration:
- Set up git pre-commit hooks
pre-commit install
As an alternative to copying auth/mtls/testdata, you can create your own example mTLS certs. See the mtls testdata readme for steps.
Reflection is included in the RPC servers (proxy and sansshell-server) allowing for the use of grpc_cli.
If you are using the certificates from above in ~/.sansshell invoking grpc_cli requires some additional flags for local testing:
$ GRPC_DEFAULT_SSL_ROOTS_FILE_PATH=$HOME/.sansshell/root.pem grpc_cli \
--ssl_client_key=$HOME/.sansshell/client.key --ssl_client_cert=$HOME/.sansshell/client.pem \
--ssl_target=127.0.0.1 --channel_creds_type=ssl ls 127.0.0.1:50043
NOTE: This connects to the proxy. Change to 50042 if you want to connect to the sansshell-server.
To run unit tests, run the following command:
go test ./...
To run integration tests, run the following command:
# Run go integration tests
INTEGRATION_TEST=yes go test -run "^TestIntegration.*$" ./...
# Run bash integration tests
./test/integration.sh
To implement integration tests, you need to:
- Create a new test file name satisfy pattern
<file-name>_integration_test.go
- Name test functions satisfy pattern
TestIntegration<FunctionName>
- Add check to skip tests when unit test is running:
if os.Getenv("INTEGRATION_TEST") == "" {
t.Skip("skipping integration test")
}
SansShell is composed of 5 primary concepts:
- A series of services, which live in the
services/
directory. - A server which wraps these services into a local host agent.
- A proxy server which can be used as an entry point to processing sansshell RPCs by validating policy and then doing fanout to 1..N actual sansshell servers. This can be done as a one to many RPC where a single incoming RPC is replicated to N backend hosts in one RPC call.
- A reference server binary, which includes all of the services.
- A CLI, which serves as the reference implementation of how to use the services via the agent.
Services implement at least one gRPC API endpoint, and expose it by calling
RegisterSansShellService
from init()
. The goal is to allow custom
implementations of the SansShell Server to easily import services they wish to
use, and have zero overhead or risk from services they do not import at compile
time.
Here you could read more about services architecture.
- Ansible: Run a local ansible playbook and return output
- Execute: Execute a command
- HealthCheck
- File operations: Read, Write, Stat, Sum, rm/rmdir, chmod/chown/chgrp and immutable operations (if OS supported).
- Package operations: Install, Upgrade, List, Repolist
- Process operations: List, Get stacks (native or Java), Get dumps (core or Java heap)
- MPA operations: Multi party authorization for commands
- Network:
- TCP-Check - Check if a TCP port is open on a remote host
- Service operations: List, Status, Start/stop/restart
TODO: Document service/.../client expectations.
Most of the logic of instantiating a local SansShell server lives in the
server
directory. This instantiates a gRPC server, registers the imported
services with that server, and constraints them with the supplied OPA policy.
There is a reference implementation of a SansShell Proxy Server in
cmd/proxy-server
, which should be suitable as-written for many use cases.
It's intentionally kept relatively short, so that it can be copied to another
repository and customized by adjusting only the imported services.
There is a reference implementation of a SansShell Server in
cmd/sansshell-server
, which should be suitable as-written for some use cases.
It's intentionally kept relatively short, so that it can be copied to another
repository and customized by adjusting only the imported services.
There is a reference implementation of a SansShell CLI Client in
cmd/sanssh
. It provides raw access to each gRPC endpoint, as well
as a way to implement "convenience" commands which chain together a series of
actions.
It also demonstrates how to set up command line completion. To use this, set the appropriate line in your shell configuration.
# In .bashrc
complete -C /path/to/sanssh -o dirnames sanssh
# Or in .zshrc
autoload -Uz compinit && compinit
autoload -U +X bashcompinit && bashcompinit
complete -C /path/to/sanssh -o dirnames sanssh
MPA, or multi party authorization, allows guarding sensitive commands behind additional approval. SansShell supports writing authorization policies that only pass when a command is approved by additional entities beyond the caller. See services/mpa/README.md for details on implementation and usage.
To try this out in the reference client, run the following commands in parallel in separate terminals. This will run a server that accepts any command from a proxy and a proxy that allows MPA requests from the "sanssh" user when approved by the "approver" user.
# Start the server
go run ./cmd/sansshell-server -server-cert ./auth/mtls/testdata/leaf.pem -server-key ./auth/mtls/testdata/leaf.key
# Start the proxy
go run ./cmd/proxy-server -client-cert ./services/mpa/testdata/proxy.pem -client-key ./services/mpa/testdata/proxy.key -server-cert ./services/mpa/testdata/proxy.pem -server-key ./services/mpa/testdata/proxy.key
# Run a command gated on MPA
go run ./cmd/sanssh -client-cert ./auth/mtls/testdata/client.pem -client-key ./auth/mtls/testdata/client.key -mpa -proxy localhost -targets localhost exec run /bin/echo hello world
# Approve the command above
go run ./cmd/sanssh -client-cert ./services/mpa/testdata/approver.pem -client-key ./services/mpa/testdata/approver.key -proxy localhost -targets localhost mpa approve 53feec22-5447f403-c0e0a419
SansShell is built on a principle of "Don't pay for what you don't use". This is advantageous in both minimizing the resources of SansShell server (binary size, memory footprint, etc) as well as reducing the security risk of running it. To accomplish that, all of the SansShell services are independent modules, which can be optionally included at build time. The reference server and client provide access to the features of all of the built-in modules, and come with exposure to all of their potential bugs and bloat.
As a result, we expect most users of SansShell would want to copy a very minimal set of the code (a handful of lines from the reference client and server), import only the modules they intend to use, and build their own derivative of SansShell with more (or less!) functionality.
That same extensibility makes it easy to add additional functionality by implementing your own module.
To quickly rebuild all binaries you can run:
$ go generate build.go
and they will be placed in a bin directory (which is ignored by git).
TODO: Add example client and server, building in different SansShell modules.
If you need to edit a proto file (to augment an existing service or create a new one) you'll need to generate proto outputs.
$ go generate tools.go
NOTE: tools.go will need to have additions to it if you add new services.