Enum Region 

pub enum Region {
    UsEast1,
    UsEast2,
    UsWest2,
    EuWest1,
    ApNortheast1,
    Unlisted(String),
}

An AWS region, closed over the five that run MicroVMs plus a named escape hatch.

See the module docs for why the five are an enum. Region::Unlisted is deliberately a variant rather than a hidden flag: a reader of a call site can see that someone opted into the trap, and a match over regions cannot forget the case exists.

Variants

UsEast1

UsEast2

UsWest2

EuWest1

ApNortheast1

Unlisted(String)

A region this client has not seen carry MicroVMs.

You are opting into the null-message trap. If this region does not run MicroVMs, the first control-plane call can answer AccessDeniedException with a null message, which an IAM denial can also produce. Constructible through Region::unlisted, which makes that uncertainty visible at the call site.

It exists because AWS adds regions faster than this list is re-read, and a client that refuses a region AWS has just launched in is its own kind of wrong. The override costs exactly the diagnostic above.

Implementations

impl Region

pub fn as_str(&self) -> &str

The wire spelling, which is also the endpoint’s middle segment.

pub fn unlisted(name: impl Into<String>) -> Region

Opts into a region this client has not seen carry MicroVMs.

This is the escape hatch, and it costs you the diagnostic. If the region does not run MicroVMs, the first control-plane call answers AccessDeniedException with a null message field, which can also mean an IAM denial (docs/PLATFORM.md, “A null-message AccessDeniedException can mean region availability or IAM”). Use it when AWS has launched MicroVMs somewhere new, and add the region to MICROVM_REGIONS in the same change.

A supported name passed here comes back as its proper variant rather than as Region::Unlisted, so unlisted("us-east-1") == Region::UsEast1 and nothing downstream has to handle two spellings of one region.

pub fn is_supported(&self) -> bool

Whether this is one of the five, rather than an opted-into unlisted name.

pub fn from_env(env: &dyn Fn(&str) -> Option<String>) -> Result<Region, Error>

The region the environment names: $AWS_REGION, then $AWS_DEFAULT_REGION, then us-east-1.

Parsed rather than accepted: an environment variable is a string, and this is the boundary where the enum cannot help. A region the client has not seen carry MicroVMs is refused with the null-message finding attached; opting in is explicit at a call site (--unlisted-region in the CLI, Region.unlisted in the bindings). env is a lookup rather than std::env::var so a caller (and a test) decides where the variables come from. The CLI’s region resolution and microvms_core::preflight::preflight both read it here.

Trait Implementations

impl Clone for Region

fn clone(&self) -> Region

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for Region

fn fmt(&self, f: &mut Formatter<'_>) -> Result<(), Error>

Formats the value using the given formatter.

impl Display for Region

fn fmt(&self, f: &mut Formatter<'_>) -> Result<(), Error>

Formats the value using the given formatter.

impl Eq for Region

impl FromStr for Region

fn from_str(name: &str) -> Result<Region, Error>

Parses one of the five, and refuses everything else.

The refusal is the point: this is the boundary a region name arrives at from a CLI flag or an environment variable, where it is still a string and the enum cannot help. A caller who genuinely wants a sixth region reaches for Region::unlisted and says so.

type Err = Error

The associated error which can be returned from parsing.

impl Hash for Region

fn hash<__H>(&self, state: &mut __H)

where __H: Hasher,

Feeds this value into the given Hasher.

fn hash_slice<H>(data: &[Self], state: &mut H)

where H: Hasher, Self: Sized,

Feeds a slice of this type into the given Hasher.

impl PartialEq for Region

fn eq(&self, other: &Region) -> bool

Equality operator ==.

fn ne(&self, other: &Rhs) -> bool

Inequality operator !=.

impl StructuralPartialEq for Region