add one shared templated agent policy and name each agent's bao entity after it

swarm-controller/src/agent_entity.rs

@@ -0,0 +1,299 @@
+//! The identity entity an agent's login lands on, named after the agent.
+//!
+//! A cert login creates an entity with a generated name and an alias named for
+//! the certificate's common name, `hive-agent-<agent>`. The shared policy
+//! ([`policy::render_shared_agent`]) reads `{{identity.entity.name}}`, so the
+//! entity has to be called `<agent>`. This module makes it so, either by
+//! creating the entity and its alias before the first login or by renaming the
+//! entity a login already created. The alias is unique per auth mount and
+//! name, so there is never a second entity to pick between.
+//!
+//! An entity's name is its access under the shared policy, so only an entity
+//! the store named itself is ever renamed ([`is_generated_name`]) and no alias
+//! is ever moved. Any other arrangement is a [`Plan::Conflict`]: nothing is
+//! written and an operator decides.
+//!
+//! Everything else here is best effort. An agent's own policy still grants it
+//! its paths, so a store that refuses these calls costs the shared policy and
+//! nothing else: the failure is logged at `warn` and the caller goes on. The
+//! grants are the `identity/` stanzas of `swarm-bao.nix`'s
+//! `controllerPolicyText`, and a controller can start before they deploy.
+
+use anyhow::{Context, Result, bail};
+use swarm_secret_client::{
+    SecretStore,
+    client::{DEFAULT_CERT_MOUNT, EntityRef},
+    policy,
+};
+
+/// What the store holds for one agent's entity.
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct Seen {
+    /// The entity that owns the agent's alias on the cert mount.
+    pub by_alias: Option<EntityRef>,
+    /// The id of the entity named after the agent.
+    pub by_name: Option<String>,
+}
+
+/// What to do about it.
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub enum Plan {
+    /// The alias's entity is already named after the agent.
+    Keep,
+    /// A login created the entity under a generated name.
+    Rename { id: String },
+    /// An entity named after the agent exists, and the alias is on no entity.
+    AddAlias { entity_id: String },
+    /// Neither the entity nor the alias exists.
+    CreateAndAlias,
+    /// The alias sits on an entity that is not the agent's: one with a name of
+    /// someone's choosing, or one while another entity already has the
+    /// agent's name. Nothing is written.
+    Conflict { alias: String, entity_name: String },
+}
+
+/// Whether `name` is one the store gave an entity at login: `entity_`, eight
+/// lowercase hex digits, and the root namespace's `.root` suffix, which stores
+/// that predate namespaces leave off.
+///
+/// Exact on purpose. A name that is merely close, such as `entity_` followed
+/// by a word, is somebody's choice of name.
+#[must_use]
+pub fn is_generated_name(name: &str) -> bool {
+    let Some(rest) = name.strip_prefix("entity_") else {
+        return false;
+    };
+    let digits = rest.strip_suffix(".root").unwrap_or(rest);
+    digits.len() == 8
+        && digits
+            .bytes()
+            .all(|b| b.is_ascii_digit() || (b'a'..=b'f').contains(&b))
+}
+
+/// The plan that leaves the alias on an entity named `agent`.
+#[must_use]
+pub fn plan(agent: &str, seen: &Seen) -> Plan {
+    match (&seen.by_alias, &seen.by_name) {
+        (Some(entity), _) if entity.name == agent => Plan::Keep,
+        (Some(entity), None) if is_generated_name(&entity.name) => Plan::Rename {
+            id: entity.id.clone(),
+        },
+        (Some(entity), _) => Plan::Conflict {
+            alias: format!("{}{agent}", policy::AGENT_PREFIX),
+            entity_name: entity.name.clone(),
+        },
+        (None, Some(named)) => Plan::AddAlias {
+            entity_id: named.clone(),
+        },
+        (None, None) => Plan::CreateAndAlias,
+    }
+}
+
+/// Make sure every agent in `agents` has its entity, logging what could not be
+/// done. Never fails: see the module header.
+pub async fn ensure_agents(store: &SecretStore, agents: &[String]) {
+    let accessor = match store.auth_mount_accessor(DEFAULT_CERT_MOUNT).await {
+        Ok(accessor) => accessor,
+        Err(e) => {
+            tracing::warn!(
+                error = %e,
+                "agent entities are not managed: the cert auth mount's accessor could not be read; agents keep their own policy"
+            );
+            return;
+        }
+    };
+    let mut changed = 0_usize;
+    for agent in agents {
+        match ensure_one(store, &accessor, agent).await {
+            Ok(Plan::Keep | Plan::Conflict { .. }) => {}
+            Ok(_) => changed += 1,
+            Err(e) => {
+                tracing::warn!(agent, error = %format!("{e:#}"), "this agent's identity entity could not be set up");
+            }
+        }
+    }
+    tracing::info!(
+        changed,
+        agents = agents.len(),
+        "agent identity entities checked"
+    );
+}
+
+/// [`ensure_agents`] for one agent.
+pub async fn ensure_agent(store: &SecretStore, agent: &str) {
+    ensure_agents(store, &[agent.to_owned()]).await;
+}
+
+/// Observe, plan and apply for one agent.
+async fn ensure_one(store: &SecretStore, accessor: &str, agent: &str) -> Result<Plan> {
+    let alias = policy::agent_object_name(agent)?;
+    let seen = Seen {
+        by_alias: store
+            .entity_by_alias(&alias, accessor)
+            .await
+            .with_context(|| format!("looking up the entity owning alias {alias}"))?,
+        by_name: store
+            .entity_id_by_name(agent)
+            .await
+            .with_context(|| format!("looking up the entity named {agent}"))?,
+    };
+    let plan = plan(agent, &seen);
+    match &plan {
+        Plan::Keep => {}
+        Plan::Rename { id } => {
+            store
+                .rename_entity(id, agent)
+                .await
+                .with_context(|| format!("renaming entity {id} to {agent}"))?;
+            tracing::info!(agent, entity = %id, "agent identity entity renamed");
+        }
+        Plan::AddAlias { entity_id } => {
+            store
+                .create_entity_alias(&alias, accessor, entity_id)
+                .await
+                .with_context(|| format!("adding alias {alias} to entity {entity_id}"))?;
+            tracing::info!(agent, entity = %entity_id, "agent identity alias added");
+        }
+        Plan::CreateAndAlias => {
+            store
+                .create_entity(agent)
+                .await
+                .with_context(|| format!("creating the entity {agent}"))?;
+            let Some(entity_id) = store.entity_id_by_name(agent).await? else {
+                bail!("the entity {agent} was created and is not there to read back");
+            };
+            store
+                .create_entity_alias(&alias, accessor, &entity_id)
+                .await
+                .with_context(|| format!("adding alias {alias} to entity {entity_id}"))?;
+            tracing::info!(agent, entity = %entity_id, "agent identity entity created");
+        }
+        Plan::Conflict { alias, entity_name } => {
+            tracing::error!(
+                agent,
+                alias,
+                entity_name,
+                "the agent's alias is on an entity that is not the agent's; nothing was changed and the agent keeps its own policy"
+            );
+        }
+    }
+    Ok(plan)
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    fn entity(id: &str, name: &str) -> EntityRef {
+        EntityRef {
+            id: id.to_owned(),
+            name: name.to_owned(),
+        }
+    }
+
+    fn conflict(entity_name: &str) -> Plan {
+        Plan::Conflict {
+            alias: "hive-agent-atlas".to_owned(),
+            entity_name: entity_name.to_owned(),
+        }
+    }
+
+    #[test]
+    fn an_entity_already_named_after_the_agent_is_kept() {
+        let seen = Seen {
+            by_alias: Some(entity("e1", "atlas")),
+            by_name: Some("e1".to_owned()),
+        };
+        assert_eq!(plan("atlas", &seen), Plan::Keep);
+    }
+
+    #[test]
+    fn nothing_at_all_is_created_with_its_alias() {
+        let seen = Seen {
+            by_alias: None,
+            by_name: None,
+        };
+        assert_eq!(plan("atlas", &seen), Plan::CreateAndAlias);
+    }
+
+    #[test]
+    fn an_entity_a_login_named_is_renamed() {
+        for generated in ["entity_1a2b3c4d.root", "entity_1a2b3c4d"] {
+            let seen = Seen {
+                by_alias: Some(entity("e1", generated)),
+                by_name: None,
+            };
+            assert_eq!(
+                plan("atlas", &seen),
+                Plan::Rename {
+                    id: "e1".to_owned()
+                },
+                "{generated}"
+            );
+        }
+    }
+
+    #[test]
+    fn an_entity_somebody_named_is_never_renamed() {
+        let seen = Seen {
+            by_alias: Some(entity("e1", "bob")),
+            by_name: None,
+        };
+        assert_eq!(plan("atlas", &seen), conflict("bob"));
+    }
+
+    #[test]
+    fn a_name_only_close_to_the_generated_shape_is_somebodys_choice() {
+        for name in [
+            "entity_",
+            "entity_backup",
+            "entity_1a2b3c4",
+            "entity_1a2b3c4d5",
+            "entity_1A2B3C4D",
+            "entity_1a2b3c4g",
+            "entity_1a2b3c4d.root2",
+            "entity_1a2b3c4d.other",
+            "entity_1a2b3c4d.root.root",
+            "xentity_1a2b3c4d",
+            "entity-1a2b3c4d",
+        ] {
+            let seen = Seen {
+                by_alias: Some(entity("e1", name)),
+                by_name: None,
+            };
+            assert_eq!(plan("atlas", &seen), conflict(name), "{name}");
+        }
+    }
+
+    #[test]
+    fn an_entity_without_the_alias_gets_it() {
+        let seen = Seen {
+            by_alias: None,
+            by_name: Some("e1".to_owned()),
+        };
+        assert_eq!(
+            plan("atlas", &seen),
+            Plan::AddAlias {
+                entity_id: "e1".to_owned()
+            }
+        );
+    }
+
+    #[test]
+    fn an_alias_on_another_entity_while_the_agents_name_is_taken_is_a_conflict() {
+        let seen = Seen {
+            by_alias: Some(entity("e1", "entity_1a2b3c4d.root")),
+            by_name: Some("e2".to_owned()),
+        };
+        assert_eq!(plan("atlas", &seen), conflict("entity_1a2b3c4d.root"));
+    }
+
+    #[test]
+    fn an_alias_on_a_foreign_entity_is_not_moved_to_the_agents() {
+        let seen = Seen {
+            by_alias: Some(entity("e1", "bob")),
+            by_name: Some("e2".to_owned()),
+        };
+        assert_eq!(plan("atlas", &seen), conflict("bob"));
+    }
+}