Merge pull request 'Add node-global lock for bucket/key operations (fix #723)' (#728) from lock-createbucket into main

Reviewed-on: https://git.deuxfleurs.fr/Deuxfleurs/garage/pulls/728

6 files changed, 426 insertions, 383 deletions

diff --git a/src/model/garage.rs b/src/model/garage.rs
index c10d64c5..fe38a760 100644
--- a/src/model/garage.rs
+++ b/src/model/garage.rs
@@ -56,6 +56,9 @@ pub struct Garage {
 	/// Table containing api keys
 	pub key_table: Arc<Table<KeyTable, TableFullReplication>>,
 
+	/// Lock to prevent concurrent modification of buckets and access keys
+	bucket_lock: tokio::sync::Mutex<()>,
+
 	/// Table containing S3 objects
 	pub object_table: Arc<Table<ObjectTable, TableShardedReplication>>,
 	/// Counting table containing object counters
@@ -343,6 +346,7 @@ impl Garage {
 			bucket_table,
 			bucket_alias_table,
 			key_table,
+			bucket_lock: tokio::sync::Mutex::new(()),
 			object_table,
 			object_counter_table,
 			mpu_table,
@@ -385,6 +389,11 @@ impl Garage {
 	pub fn key_helper(&self) -> helper::key::KeyHelper {
 		helper::key::KeyHelper(self)
 	}
+
+	pub async fn locked_helper(&self) -> helper::locked::LockedHelper {
+		let lock = self.bucket_lock.lock().await;
+		helper::locked::LockedHelper(self, lock)
+	}
 }
 
 #[cfg(feature = "k2v")]
diff --git a/src/model/helper/bucket.rs b/src/model/helper/bucket.rs
index e9842a91..f4e669c3 100644
--- a/src/model/helper/bucket.rs
+++ b/src/model/helper/bucket.rs
@@ -1,19 +1,15 @@
 use std::time::Duration;
 
-use garage_util::crdt::*;
 use garage_util::data::*;
-use garage_util::error::{Error as GarageError, OkOrMessage};
+use garage_util::error::OkOrMessage;
 use garage_util::time::*;
 
 use garage_table::util::*;
 
-use crate::bucket_alias_table::*;
 use crate::bucket_table::*;
 use crate::garage::Garage;
 use crate::helper::error::*;
-use crate::helper::key::KeyHelper;
 use crate::key_table::*;
-use crate::permission::BucketKeyPerm;
 use crate::s3::object_table::*;
 
 pub struct BucketHelper<'a>(pub(crate) &'a Garage);
@@ -96,341 +92,7 @@ impl<'a> BucketHelper<'a> {
 			.ok_or_else(|| Error::NoSuchBucket(hex::encode(bucket_id)))
 	}
 
-	/// Sets a new alias for a bucket in global namespace.
-	/// This function fails if:
-	/// - alias name is not valid according to S3 spec
-	/// - bucket does not exist or is deleted
-	/// - alias already exists and points to another bucket
-	pub async fn set_global_bucket_alias(
-		&self,
-		bucket_id: Uuid,
-		alias_name: &String,
-	) -> Result<(), Error> {
-		if !is_valid_bucket_name(alias_name) {
-			return Err(Error::InvalidBucketName(alias_name.to_string()));
-		}
-
-		let mut bucket = self.get_existing_bucket(bucket_id).await?;
-
-		let alias = self.0.bucket_alias_table.get(&EmptyKey, alias_name).await?;
-
-		if let Some(existing_alias) = alias.as_ref() {
-			if let Some(p_bucket) = existing_alias.state.get() {
-				if *p_bucket != bucket_id {
-					return Err(Error::BadRequest(format!(
-						"Alias {} already exists and points to different bucket: {:?}",
-						alias_name, p_bucket
-					)));
-				}
-			}
-		}
-
-		// Checks ok, add alias
-		let bucket_p = bucket.state.as_option_mut().unwrap();
-
-		let alias_ts = increment_logical_clock_2(
-			bucket_p.aliases.get_timestamp(alias_name),
-			alias.as_ref().map(|a| a.state.timestamp()).unwrap_or(0),
-		);
-
-		// ---- timestamp-ensured causality barrier ----
-		// writes are now done and all writes use timestamp alias_ts
-
-		let alias = match alias {
-			None => BucketAlias::new(alias_name.clone(), alias_ts, Some(bucket_id))
-				.ok_or_else(|| Error::InvalidBucketName(alias_name.clone()))?,
-			Some(mut a) => {
-				a.state = Lww::raw(alias_ts, Some(bucket_id));
-				a
-			}
-		};
-		self.0.bucket_alias_table.insert(&alias).await?;
-
-		bucket_p.aliases = LwwMap::raw_item(alias_name.clone(), alias_ts, true);
-		self.0.bucket_table.insert(&bucket).await?;
-
-		Ok(())
-	}
-
-	/// Unsets an alias for a bucket in global namespace.
-	/// This function fails if:
-	/// - bucket does not exist or is deleted
-	/// - alias does not exist or maps to another bucket (-> internal error)
-	/// - bucket has no other aliases (global or local)
-	pub async fn unset_global_bucket_alias(
-		&self,
-		bucket_id: Uuid,
-		alias_name: &String,
-	) -> Result<(), Error> {
-		let mut bucket = self.get_existing_bucket(bucket_id).await?;
-		let bucket_state = bucket.state.as_option_mut().unwrap();
-
-		let mut alias = self
-			.0
-			.bucket_alias_table
-			.get(&EmptyKey, alias_name)
-			.await?
-			.filter(|a| a.state.get().map(|x| x == bucket_id).unwrap_or(false))
-			.ok_or_message(format!(
-				"Internal error: alias not found or does not point to bucket {:?}",
-				bucket_id
-			))?;
-
-		let has_other_global_aliases = bucket_state
-			.aliases
-			.items()
-			.iter()
-			.any(|(name, _, active)| name != alias_name && *active);
-		let has_other_local_aliases = bucket_state
-			.local_aliases
-			.items()
-			.iter()
-			.any(|(_, _, active)| *active);
-		if !has_other_global_aliases && !has_other_local_aliases {
-			return Err(Error::BadRequest(format!("Bucket {} doesn't have other aliases, please delete it instead of just unaliasing.", alias_name)));
-		}
-
-		// Checks ok, remove alias
-		let alias_ts = increment_logical_clock_2(
-			alias.state.timestamp(),
-			bucket_state.aliases.get_timestamp(alias_name),
-		);
-
-		// ---- timestamp-ensured causality barrier ----
-		// writes are now done and all writes use timestamp alias_ts
-
-		alias.state = Lww::raw(alias_ts, None);
-		self.0.bucket_alias_table.insert(&alias).await?;
-
-		bucket_state.aliases = LwwMap::raw_item(alias_name.clone(), alias_ts, false);
-		self.0.bucket_table.insert(&bucket).await?;
-
-		Ok(())
-	}
-
-	/// Ensures a bucket does not have a certain global alias.
-	/// Contrarily to unset_global_bucket_alias, this does not
-	/// fail on any condition other than:
-	/// - bucket cannot be found (its fine if it is in deleted state)
-	/// - alias cannot be found (its fine if it points to nothing or
-	///   to another bucket)
-	pub async fn purge_global_bucket_alias(
-		&self,
-		bucket_id: Uuid,
-		alias_name: &String,
-	) -> Result<(), Error> {
-		let mut bucket = self.get_internal_bucket(bucket_id).await?;
-
-		let mut alias = self
-			.0
-			.bucket_alias_table
-			.get(&EmptyKey, alias_name)
-			.await?
-			.ok_or_else(|| Error::NoSuchBucket(alias_name.to_string()))?;
-
-		// Checks ok, remove alias
-		let alias_ts = match bucket.state.as_option() {
-			Some(bucket_state) => increment_logical_clock_2(
-				alias.state.timestamp(),
-				bucket_state.aliases.get_timestamp(alias_name),
-			),
-			None => increment_logical_clock(alias.state.timestamp()),
-		};
-
-		// ---- timestamp-ensured causality barrier ----
-		// writes are now done and all writes use timestamp alias_ts
-
-		if alias.state.get() == &Some(bucket_id) {
-			alias.state = Lww::raw(alias_ts, None);
-			self.0.bucket_alias_table.insert(&alias).await?;
-		}
-
-		if let Some(bucket_state) = bucket.state.as_option_mut() {
-			bucket_state.aliases = LwwMap::raw_item(alias_name.clone(), alias_ts, false);
-			self.0.bucket_table.insert(&bucket).await?;
-		}
-
-		Ok(())
-	}
-
-	/// Sets a new alias for a bucket in the local namespace of a key.
-	/// This function fails if:
-	/// - alias name is not valid according to S3 spec
-	/// - bucket does not exist or is deleted
-	/// - key does not exist or is deleted
-	/// - alias already exists and points to another bucket
-	pub async fn set_local_bucket_alias(
-		&self,
-		bucket_id: Uuid,
-		key_id: &String,
-		alias_name: &String,
-	) -> Result<(), Error> {
-		let key_helper = KeyHelper(self.0);
-
-		if !is_valid_bucket_name(alias_name) {
-			return Err(Error::InvalidBucketName(alias_name.to_string()));
-		}
-
-		let mut bucket = self.get_existing_bucket(bucket_id).await?;
-		let mut key = key_helper.get_existing_key(key_id).await?;
-
-		let key_param = key.state.as_option_mut().unwrap();
-
-		if let Some(Some(existing_alias)) = key_param.local_aliases.get(alias_name) {
-			if *existing_alias != bucket_id {
-				return Err(Error::BadRequest(format!("Alias {} already exists in namespace of key {} and points to different bucket: {:?}", alias_name,  key.key_id, existing_alias)));
-			}
-		}
-
-		// Checks ok, add alias
-		let bucket_p = bucket.state.as_option_mut().unwrap();
-		let bucket_p_local_alias_key = (key.key_id.clone(), alias_name.clone());
-
-		// Calculate the timestamp to assign to this aliasing in the two local_aliases maps
-		// (the one from key to bucket, and the reverse one stored in the bucket iself)
-		// so that merges on both maps in case of a concurrent operation resolve
-		// to the same alias being set
-		let alias_ts = increment_logical_clock_2(
-			key_param.local_aliases.get_timestamp(alias_name),
-			bucket_p
-				.local_aliases
-				.get_timestamp(&bucket_p_local_alias_key),
-		);
-
-		// ---- timestamp-ensured causality barrier ----
-		// writes are now done and all writes use timestamp alias_ts
-
-		key_param.local_aliases = LwwMap::raw_item(alias_name.clone(), alias_ts, Some(bucket_id));
-		self.0.key_table.insert(&key).await?;
-
-		bucket_p.local_aliases = LwwMap::raw_item(bucket_p_local_alias_key, alias_ts, true);
-		self.0.bucket_table.insert(&bucket).await?;
-
-		Ok(())
-	}
-
-	/// Unsets an alias for a bucket in the local namespace of a key.
-	/// This function fails if:
-	/// - bucket does not exist or is deleted
-	/// - key does not exist or is deleted
-	/// - alias does not exist or maps to another bucket (-> internal error)
-	/// - bucket has no other aliases (global or local)
-	pub async fn unset_local_bucket_alias(
-		&self,
-		bucket_id: Uuid,
-		key_id: &String,
-		alias_name: &String,
-	) -> Result<(), Error> {
-		let key_helper = KeyHelper(self.0);
-
-		let mut bucket = self.get_existing_bucket(bucket_id).await?;
-		let mut key = key_helper.get_existing_key(key_id).await?;
-
-		let bucket_p = bucket.state.as_option_mut().unwrap();
-
-		if key
-			.state
-			.as_option()
-			.unwrap()
-			.local_aliases
-			.get(alias_name)
-			.cloned()
-			.flatten() != Some(bucket_id)
-		{
-			return Err(GarageError::Message(format!(
-				"Bucket {:?} does not have alias {} in namespace of key {}",
-				bucket_id, alias_name, key_id
-			))
-			.into());
-		}
-
-		let has_other_global_aliases = bucket_p
-			.aliases
-			.items()
-			.iter()
-			.any(|(_, _, active)| *active);
-		let has_other_local_aliases = bucket_p
-			.local_aliases
-			.items()
-			.iter()
-			.any(|((k, n), _, active)| *k == key.key_id && n == alias_name && *active);
-		if !has_other_global_aliases && !has_other_local_aliases {
-			return Err(Error::BadRequest(format!("Bucket {} doesn't have other aliases, please delete it instead of just unaliasing.", alias_name)));
-		}
-
-		// Checks ok, remove alias
-		let key_param = key.state.as_option_mut().unwrap();
-		let bucket_p_local_alias_key = (key.key_id.clone(), alias_name.clone());
-
-		let alias_ts = increment_logical_clock_2(
-			key_param.local_aliases.get_timestamp(alias_name),
-			bucket_p
-				.local_aliases
-				.get_timestamp(&bucket_p_local_alias_key),
-		);
-
-		// ---- timestamp-ensured causality barrier ----
-		// writes are now done and all writes use timestamp alias_ts
-
-		key_param.local_aliases = LwwMap::raw_item(alias_name.clone(), alias_ts, None);
-		self.0.key_table.insert(&key).await?;
-
-		bucket_p.local_aliases = LwwMap::raw_item(bucket_p_local_alias_key, alias_ts, false);
-		self.0.bucket_table.insert(&bucket).await?;
-
-		Ok(())
-	}
-
-	/// Sets permissions for a key on a bucket.
-	/// This function fails if:
-	/// - bucket or key cannot be found at all (its ok if they are in deleted state)
-	/// - bucket or key is in deleted state and we are trying to set permissions other than "deny
-	/// all"
-	pub async fn set_bucket_key_permissions(
-		&self,
-		bucket_id: Uuid,
-		key_id: &String,
-		mut perm: BucketKeyPerm,
-	) -> Result<(), Error> {
-		let key_helper = KeyHelper(self.0);
-
-		let mut bucket = self.get_internal_bucket(bucket_id).await?;
-		let mut key = key_helper.get_internal_key(key_id).await?;
-
-		if let Some(bstate) = bucket.state.as_option() {
-			if let Some(kp) = bstate.authorized_keys.get(key_id) {
-				perm.timestamp = increment_logical_clock_2(perm.timestamp, kp.timestamp);
-			}
-		} else if perm.is_any() {
-			return Err(Error::BadRequest(
-				"Trying to give permissions on a deleted bucket".into(),
-			));
-		}
-
-		if let Some(kstate) = key.state.as_option() {
-			if let Some(bp) = kstate.authorized_buckets.get(&bucket_id) {
-				perm.timestamp = increment_logical_clock_2(perm.timestamp, bp.timestamp);
-			}
-		} else if perm.is_any() {
-			return Err(Error::BadRequest(
-				"Trying to give permissions to a deleted key".into(),
-			));
-		}
-
-		// ---- timestamp-ensured causality barrier ----
-
-		if let Some(bstate) = bucket.state.as_option_mut() {
-			bstate.authorized_keys = Map::put_mutator(key_id.clone(), perm);
-			self.0.bucket_table.insert(&bucket).await?;
-		}
-
-		if let Some(kstate) = key.state.as_option_mut() {
-			kstate.authorized_buckets = Map::put_mutator(bucket_id, perm);
-			self.0.key_table.insert(&key).await?;
-		}
-
-		Ok(())
-	}
+	// ----
 
 	pub async fn is_bucket_empty(&self, bucket_id: Uuid) -> Result<bool, Error> {
 		let objects = self
diff --git a/src/model/helper/key.rs b/src/model/helper/key.rs
index c1a8e974..b8a99d55 100644
--- a/src/model/helper/key.rs
+++ b/src/model/helper/key.rs
@@ -1,12 +1,9 @@
 use garage_table::util::*;
-use garage_util::crdt::*;
 use garage_util::error::OkOrMessage;
 
 use crate::garage::Garage;
-use crate::helper::bucket::BucketHelper;
 use crate::helper::error::*;
 use crate::key_table::{Key, KeyFilter};
-use crate::permission::BucketKeyPerm;
 
 pub struct KeyHelper<'a>(pub(crate) &'a Garage);
 
@@ -65,38 +62,4 @@ impl<'a> KeyHelper<'a> {
 			Ok(candidates.into_iter().next().unwrap())
 		}
 	}
-
-	/// Deletes an API access key
-	pub async fn delete_key(&self, key: &mut Key) -> Result<(), Error> {
-		let bucket_helper = BucketHelper(self.0);
-
-		let state = key.state.as_option_mut().unwrap();
-
-		// --- done checking, now commit ---
-		// (the step at unset_local_bucket_alias will fail if a bucket
-		// does not have another alias, the deletion will be
-		// interrupted in the middle if that happens)
-
-		// 1. Delete local aliases
-		for (alias, _, to) in state.local_aliases.items().iter() {
-			if let Some(bucket_id) = to {
-				bucket_helper
-					.unset_local_bucket_alias(*bucket_id, &key.key_id, alias)
-					.await?;
-			}
-		}
-
-		// 2. Remove permissions on all authorized buckets
-		for (ab_id, _auth) in state.authorized_buckets.items().iter() {
-			bucket_helper
-				.set_bucket_key_permissions(*ab_id, &key.key_id, BucketKeyPerm::NO_PERMISSIONS)
-				.await?;
-		}
-
-		// 3. Actually delete key
-		key.state = Deletable::delete();
-		self.0.key_table.insert(key).await?;
-
-		Ok(())
-	}
 }
diff --git a/src/model/helper/locked.rs b/src/model/helper/locked.rs
new file mode 100644
index 00000000..f8e06add
--- /dev/null
+++ b/src/model/helper/locked.rs
@@ -0,0 +1,410 @@
+use garage_util::crdt::*;
+use garage_util::data::*;
+use garage_util::error::{Error as GarageError, OkOrMessage};
+use garage_util::time::*;
+
+use garage_table::util::*;
+
+use crate::bucket_alias_table::*;
+use crate::garage::Garage;
+use crate::helper::bucket::BucketHelper;
+use crate::helper::error::*;
+use crate::helper::key::KeyHelper;
+use crate::key_table::*;
+use crate::permission::BucketKeyPerm;
+
+/// A LockedHelper is the mandatory struct to hold when doing operations
+/// that modify access keys or bucket aliases. This structure takes
+/// a lock to a unit value that is in the globally-shared Garage struct.
+///
+/// This avoid several concurrent requests to modify the list of buckets
+/// and aliases at the same time, ending up in inconsistent states.
+/// This DOES NOT FIX THE FUNDAMENTAL ISSUE as CreateBucket requests handled
+/// by different API nodes can still break the cluster, but it is a first
+/// fix that allows consistency to be maintained if all such requests are
+/// directed to a single node, which is doable for many deployments.
+///
+/// See issues: #649, #723
+pub struct LockedHelper<'a>(
+	pub(crate) &'a Garage,
+	pub(crate) tokio::sync::MutexGuard<'a, ()>,
+);
+
+#[allow(clippy::ptr_arg)]
+impl<'a> LockedHelper<'a> {
+	pub fn bucket(&self) -> BucketHelper<'a> {
+		BucketHelper(self.0)
+	}
+
+	pub fn key(&self) -> KeyHelper<'a> {
+		KeyHelper(self.0)
+	}
+
+	/// Sets a new alias for a bucket in global namespace.
+	/// This function fails if:
+	/// - alias name is not valid according to S3 spec
+	/// - bucket does not exist or is deleted
+	/// - alias already exists and points to another bucket
+	pub async fn set_global_bucket_alias(
+		&self,
+		bucket_id: Uuid,
+		alias_name: &String,
+	) -> Result<(), Error> {
+		if !is_valid_bucket_name(alias_name) {
+			return Err(Error::InvalidBucketName(alias_name.to_string()));
+		}
+
+		let mut bucket = self.bucket().get_existing_bucket(bucket_id).await?;
+
+		let alias = self.0.bucket_alias_table.get(&EmptyKey, alias_name).await?;
+
+		if let Some(existing_alias) = alias.as_ref() {
+			if let Some(p_bucket) = existing_alias.state.get() {
+				if *p_bucket != bucket_id {
+					return Err(Error::BadRequest(format!(
+						"Alias {} already exists and points to different bucket: {:?}",
+						alias_name, p_bucket
+					)));
+				}
+			}
+		}
+
+		// Checks ok, add alias
+		let bucket_p = bucket.state.as_option_mut().unwrap();
+
+		let alias_ts = increment_logical_clock_2(
+			bucket_p.aliases.get_timestamp(alias_name),
+			alias.as_ref().map(|a| a.state.timestamp()).unwrap_or(0),
+		);
+
+		// ---- timestamp-ensured causality barrier ----
+		// writes are now done and all writes use timestamp alias_ts
+
+		let alias = match alias {
+			None => BucketAlias::new(alias_name.clone(), alias_ts, Some(bucket_id))
+				.ok_or_else(|| Error::InvalidBucketName(alias_name.clone()))?,
+			Some(mut a) => {
+				a.state = Lww::raw(alias_ts, Some(bucket_id));
+				a
+			}
+		};
+		self.0.bucket_alias_table.insert(&alias).await?;
+
+		bucket_p.aliases = LwwMap::raw_item(alias_name.clone(), alias_ts, true);
+		self.0.bucket_table.insert(&bucket).await?;
+
+		Ok(())
+	}
+
+	/// Unsets an alias for a bucket in global namespace.
+	/// This function fails if:
+	/// - bucket does not exist or is deleted
+	/// - alias does not exist or maps to another bucket (-> internal error)
+	/// - bucket has no other aliases (global or local)
+	pub async fn unset_global_bucket_alias(
+		&self,
+		bucket_id: Uuid,
+		alias_name: &String,
+	) -> Result<(), Error> {
+		let mut bucket = self.bucket().get_existing_bucket(bucket_id).await?;
+		let bucket_state = bucket.state.as_option_mut().unwrap();
+
+		let mut alias = self
+			.0
+			.bucket_alias_table
+			.get(&EmptyKey, alias_name)
+			.await?
+			.filter(|a| a.state.get().map(|x| x == bucket_id).unwrap_or(false))
+			.ok_or_message(format!(
+				"Internal error: alias not found or does not point to bucket {:?}",
+				bucket_id
+			))?;
+
+		let has_other_global_aliases = bucket_state
+			.aliases
+			.items()
+			.iter()
+			.any(|(name, _, active)| name != alias_name && *active);
+		let has_other_local_aliases = bucket_state
+			.local_aliases
+			.items()
+			.iter()
+			.any(|(_, _, active)| *active);
+		if !has_other_global_aliases && !has_other_local_aliases {
+			return Err(Error::BadRequest(format!("Bucket {} doesn't have other aliases, please delete it instead of just unaliasing.", alias_name)));
+		}
+
+		// Checks ok, remove alias
+		let alias_ts = increment_logical_clock_2(
+			alias.state.timestamp(),
+			bucket_state.aliases.get_timestamp(alias_name),
+		);
+
+		// ---- timestamp-ensured causality barrier ----
+		// writes are now done and all writes use timestamp alias_ts
+
+		alias.state = Lww::raw(alias_ts, None);
+		self.0.bucket_alias_table.insert(&alias).await?;
+
+		bucket_state.aliases = LwwMap::raw_item(alias_name.clone(), alias_ts, false);
+		self.0.bucket_table.insert(&bucket).await?;
+
+		Ok(())
+	}
+
+	/// Ensures a bucket does not have a certain global alias.
+	/// Contrarily to unset_global_bucket_alias, this does not
+	/// fail on any condition other than:
+	/// - bucket cannot be found (its fine if it is in deleted state)
+	/// - alias cannot be found (its fine if it points to nothing or
+	///   to another bucket)
+	pub async fn purge_global_bucket_alias(
+		&self,
+		bucket_id: Uuid,
+		alias_name: &String,
+	) -> Result<(), Error> {
+		let mut bucket = self.bucket().get_internal_bucket(bucket_id).await?;
+
+		let mut alias = self
+			.0
+			.bucket_alias_table
+			.get(&EmptyKey, alias_name)
+			.await?
+			.ok_or_else(|| Error::NoSuchBucket(alias_name.to_string()))?;
+
+		// Checks ok, remove alias
+		let alias_ts = match bucket.state.as_option() {
+			Some(bucket_state) => increment_logical_clock_2(
+				alias.state.timestamp(),
+				bucket_state.aliases.get_timestamp(alias_name),
+			),
+			None => increment_logical_clock(alias.state.timestamp()),
+		};
+
+		// ---- timestamp-ensured causality barrier ----
+		// writes are now done and all writes use timestamp alias_ts
+
+		if alias.state.get() == &Some(bucket_id) {
+			alias.state = Lww::raw(alias_ts, None);
+			self.0.bucket_alias_table.insert(&alias).await?;
+		}
+
+		if let Some(bucket_state) = bucket.state.as_option_mut() {
+			bucket_state.aliases = LwwMap::raw_item(alias_name.clone(), alias_ts, false);
+			self.0.bucket_table.insert(&bucket).await?;
+		}
+
+		Ok(())
+	}
+
+	/// Sets a new alias for a bucket in the local namespace of a key.
+	/// This function fails if:
+	/// - alias name is not valid according to S3 spec
+	/// - bucket does not exist or is deleted
+	/// - key does not exist or is deleted
+	/// - alias already exists and points to another bucket
+	pub async fn set_local_bucket_alias(
+		&self,
+		bucket_id: Uuid,
+		key_id: &String,
+		alias_name: &String,
+	) -> Result<(), Error> {
+		let key_helper = KeyHelper(self.0);
+
+		if !is_valid_bucket_name(alias_name) {
+			return Err(Error::InvalidBucketName(alias_name.to_string()));
+		}
+
+		let mut bucket = self.bucket().get_existing_bucket(bucket_id).await?;
+		let mut key = key_helper.get_existing_key(key_id).await?;
+
+		let key_param = key.state.as_option_mut().unwrap();
+
+		if let Some(Some(existing_alias)) = key_param.local_aliases.get(alias_name) {
+			if *existing_alias != bucket_id {
+				return Err(Error::BadRequest(format!("Alias {} already exists in namespace of key {} and points to different bucket: {:?}", alias_name,  key.key_id, existing_alias)));
+			}
+		}
+
+		// Checks ok, add alias
+		let bucket_p = bucket.state.as_option_mut().unwrap();
+		let bucket_p_local_alias_key = (key.key_id.clone(), alias_name.clone());
+
+		// Calculate the timestamp to assign to this aliasing in the two local_aliases maps
+		// (the one from key to bucket, and the reverse one stored in the bucket iself)
+		// so that merges on both maps in case of a concurrent operation resolve
+		// to the same alias being set
+		let alias_ts = increment_logical_clock_2(
+			key_param.local_aliases.get_timestamp(alias_name),
+			bucket_p
+				.local_aliases
+				.get_timestamp(&bucket_p_local_alias_key),
+		);
+
+		// ---- timestamp-ensured causality barrier ----
+		// writes are now done and all writes use timestamp alias_ts
+
+		key_param.local_aliases = LwwMap::raw_item(alias_name.clone(), alias_ts, Some(bucket_id));
+		self.0.key_table.insert(&key).await?;
+
+		bucket_p.local_aliases = LwwMap::raw_item(bucket_p_local_alias_key, alias_ts, true);
+		self.0.bucket_table.insert(&bucket).await?;
+
+		Ok(())
+	}
+
+	/// Unsets an alias for a bucket in the local namespace of a key.
+	/// This function fails if:
+	/// - bucket does not exist or is deleted
+	/// - key does not exist or is deleted
+	/// - alias does not exist or maps to another bucket (-> internal error)
+	/// - bucket has no other aliases (global or local)
+	pub async fn unset_local_bucket_alias(
+		&self,
+		bucket_id: Uuid,
+		key_id: &String,
+		alias_name: &String,
+	) -> Result<(), Error> {
+		let key_helper = KeyHelper(self.0);
+
+		let mut bucket = self.bucket().get_existing_bucket(bucket_id).await?;
+		let mut key = key_helper.get_existing_key(key_id).await?;
+
+		let bucket_p = bucket.state.as_option_mut().unwrap();
+
+		if key
+			.state
+			.as_option()
+			.unwrap()
+			.local_aliases
+			.get(alias_name)
+			.cloned()
+			.flatten() != Some(bucket_id)
+		{
+			return Err(GarageError::Message(format!(
+				"Bucket {:?} does not have alias {} in namespace of key {}",
+				bucket_id, alias_name, key_id
+			))
+			.into());
+		}
+
+		let has_other_global_aliases = bucket_p
+			.aliases
+			.items()
+			.iter()
+			.any(|(_, _, active)| *active);
+		let has_other_local_aliases = bucket_p
+			.local_aliases
+			.items()
+			.iter()
+			.any(|((k, n), _, active)| *k == key.key_id && n == alias_name && *active);
+		if !has_other_global_aliases && !has_other_local_aliases {
+			return Err(Error::BadRequest(format!("Bucket {} doesn't have other aliases, please delete it instead of just unaliasing.", alias_name)));
+		}
+
+		// Checks ok, remove alias
+		let key_param = key.state.as_option_mut().unwrap();
+		let bucket_p_local_alias_key = (key.key_id.clone(), alias_name.clone());
+
+		let alias_ts = increment_logical_clock_2(
+			key_param.local_aliases.get_timestamp(alias_name),
+			bucket_p
+				.local_aliases
+				.get_timestamp(&bucket_p_local_alias_key),
+		);
+
+		// ---- timestamp-ensured causality barrier ----
+		// writes are now done and all writes use timestamp alias_ts
+
+		key_param.local_aliases = LwwMap::raw_item(alias_name.clone(), alias_ts, None);
+		self.0.key_table.insert(&key).await?;
+
+		bucket_p.local_aliases = LwwMap::raw_item(bucket_p_local_alias_key, alias_ts, false);
+		self.0.bucket_table.insert(&bucket).await?;
+
+		Ok(())
+	}
+
+	/// Sets permissions for a key on a bucket.
+	/// This function fails if:
+	/// - bucket or key cannot be found at all (its ok if they are in deleted state)
+	/// - bucket or key is in deleted state and we are trying to set permissions other than "deny
+	/// all"
+	pub async fn set_bucket_key_permissions(
+		&self,
+		bucket_id: Uuid,
+		key_id: &String,
+		mut perm: BucketKeyPerm,
+	) -> Result<(), Error> {
+		let key_helper = KeyHelper(self.0);
+
+		let mut bucket = self.bucket().get_internal_bucket(bucket_id).await?;
+		let mut key = key_helper.get_internal_key(key_id).await?;
+
+		if let Some(bstate) = bucket.state.as_option() {
+			if let Some(kp) = bstate.authorized_keys.get(key_id) {
+				perm.timestamp = increment_logical_clock_2(perm.timestamp, kp.timestamp);
+			}
+		} else if perm.is_any() {
+			return Err(Error::BadRequest(
+				"Trying to give permissions on a deleted bucket".into(),
+			));
+		}
+
+		if let Some(kstate) = key.state.as_option() {
+			if let Some(bp) = kstate.authorized_buckets.get(&bucket_id) {
+				perm.timestamp = increment_logical_clock_2(perm.timestamp, bp.timestamp);
+			}
+		} else if perm.is_any() {
+			return Err(Error::BadRequest(
+				"Trying to give permissions to a deleted key".into(),
+			));
+		}
+
+		// ---- timestamp-ensured causality barrier ----
+
+		if let Some(bstate) = bucket.state.as_option_mut() {
+			bstate.authorized_keys = Map::put_mutator(key_id.clone(), perm);
+			self.0.bucket_table.insert(&bucket).await?;
+		}
+
+		if let Some(kstate) = key.state.as_option_mut() {
+			kstate.authorized_buckets = Map::put_mutator(bucket_id, perm);
+			self.0.key_table.insert(&key).await?;
+		}
+
+		Ok(())
+	}
+
+	// ----
+
+	/// Deletes an API access key
+	pub async fn delete_key(&self, key: &mut Key) -> Result<(), Error> {
+		let state = key.state.as_option_mut().unwrap();
+
+		// --- done checking, now commit ---
+		// (the step at unset_local_bucket_alias will fail if a bucket
+		// does not have another alias, the deletion will be
+		// interrupted in the middle if that happens)
+
+		// 1. Delete local aliases
+		for (alias, _, to) in state.local_aliases.items().iter() {
+			if let Some(bucket_id) = to {
+				self.unset_local_bucket_alias(*bucket_id, &key.key_id, alias)
+					.await?;
+			}
+		}
+
+		// 2. Remove permissions on all authorized buckets
+		for (ab_id, _auth) in state.authorized_buckets.items().iter() {
+			self.set_bucket_key_permissions(*ab_id, &key.key_id, BucketKeyPerm::NO_PERMISSIONS)
+				.await?;
+		}
+
+		// 3. Actually delete key
+		key.state = Deletable::delete();
+		self.0.key_table.insert(key).await?;
+
+		Ok(())
+	}
+}
diff --git a/src/model/helper/mod.rs b/src/model/helper/mod.rs
index dd947c86..5534ae3d 100644
--- a/src/model/helper/mod.rs
+++ b/src/model/helper/mod.rs
@@ -1,3 +1,4 @@
 pub mod bucket;
 pub mod error;
 pub mod key;
+pub mod locked;
diff --git a/src/model/migrate.rs b/src/model/migrate.rs
index 4c74b43b..8528382a 100644
--- a/src/model/migrate.rs
+++ b/src/model/migrate.rs
@@ -67,6 +67,8 @@ impl Migrate {
 			None
 		};
 
+		let helper = self.garage.locked_helper().await;
+
 		self.garage
 			.bucket_table
 			.insert(&Bucket {
@@ -84,14 +86,10 @@ impl Migrate {
 			})
 			.await?;
 
-		self.garage
-			.bucket_helper()
-			.set_global_bucket_alias(bucket_id, &new_name)
-			.await?;
+		helper.set_global_bucket_alias(bucket_id, &new_name).await?;
 
 		for (k, ts, perm) in old_bucket_p.authorized_keys.items().iter() {
-			self.garage
-				.bucket_helper()
+			helper
 				.set_bucket_key_permissions(
 					bucket_id,
 					k,