Albatross: orchestrate and manage MirageOS unikernels with Solo5

The goal of albatross is robust deployment of MirageOS unikernels using Solo5, including precise error handling of failures. The code running under superuser privileges is minimimal. Albatross is supposed to be run on a machine in the dom0, next to the hypervisor. Albatross keeps track of unikernel resource usage (memory, CPUs, bridges, block storage and active block devices). Policies restricting these resources for administrative domains are available. Local and remote deployments are supported, remote ones are authenticated and encrypted via a mutually authenticated TLS connection using X.509 client certificates. Multi-tenancy deployments are possible, tenants do not need any other access to the machine: console output and statistics gathered by the host are accessible via TLS. Albatross keeps the information of running unikernels persistently, and starts these unikernels when the albatross daemon is started. This means that whenever a unikernel was started, it keeps running until it crashes or an explicit destroy command is issued.

The administrative domain is similar to DNS: each unikernel has a name (e.g. foo.hello), which consists of labels separated by dots. Policies and access is done on a name basis - if access to foo is granted, foo.hello, foo.bar.hello, etc. can be accessed, but not bar or bar.hello.

Components

Albatross consists of a set of binaries. Several daemons, which communicate in a request-response style over Unix domain sockets, are run in the host system:

• vmmd: privileged to create and destroy unikernels
• vmmd_console: reads the console output of unikernels
• vmmd_log: event log
• vmmd_stats: statistics gathering (rusage, ifstat, BHyve debug counters)
• vmmd_tls: remote deployment via TLS with client certificate, and proxies to local daemons
• vmmd_tls_inetd: remote deployment via TLS and inetd (alternative to vmmd_tls)
• vmmd_influx: statistic reporting from vmmd_stats to influx

The main daemon is the privileged vmmd, which supervises unikernels. It opens a listening Unix domain socket, reads the persisted unikernel configuration, starts these unikernels, and awaits commands. Access can be regulated by Unix file permissions, only those users who can write to that socket can send commands.

Vmmd_console does not keep any persistent state, but a ring buffer of console output from each unikernel. These messages can be retrieved by a client, as a stream of messages (history, and whenever a new line is output, it is send to the interested client). Each unikernel output can only be read by a single client, to avoid amplification of traffic if lots of clients are connected. Vmmd sends a message to vmmd_console whenever a new unikernel is started, upon reception Vmmd_console opens and reads the fifo which the unikernel will write their standard output to.

Vmmd_log keeps a persistent event log for albatross, can be read by clients.

Vmmd_stats gathers periodically statistics (memory, CPU, network, hypervisor) from all running unikernels.

Vmmd_tls and vmmd_tls_inetd listen on a TCP port, and proxy requests from remote clients to the respective daemons described above. They enforce client authentication, and use the commen names of the client certificate chain as administrative domain. The policies are embedded in CA certificates, the command is embedded in the leaf certificate.

The following command-line applications for local and remote management are provided:

• vmmc_local: sends a command locally to the Unix domain sockets
• vmmc_remote: connects to a remote TLS endpoint and sends a command
• vmmp_request: creates a certificate signing request containing a command
• vmmp_ca: certificate authority operations: sign, generate, and revoke (NYI)
• vmmc_bistro: command line utility to execute a command remotely: request, sign, remote (do not use in production, requires CA key locally)

Installation

To install Albatross, run opam pin add albatross https://github.com/hannesm/albatross.

Init scripts for FreeBSD are provided in the packaging/rc.d subdirectory.

TODO: from here on, this documentation is not up to date.

It may help to read the outdated blog article for motivation of albatross and an overview over its functionality.