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pageserver config + remote_storage config: ignore unknown fields (instead of deny_unknown_fields)

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refs
- refs https://github.com/neondatabase/neon/issues/8915
This commit is contained in:
Christian Schwarz
2025-03-19 18:37:04 +01:00
parent 019a29748d
commit 13fa4b48c3
3 changed files with 48 additions and 86 deletions
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libs/pageserver_api/src/config.rs
+47 -6
View File
@@ -51,9 +51,54 @@ pub struct NodeMetadata {
/// If there cannot be a static default value because we need to make runtime
/// checks to determine the default, make it an `Option` (which defaults to None).
/// The runtime check should be done in the consuming crate, i.e., `pageserver`.
///
/// Unknown fields are silently ignored during deserialization.
/// The alternative, which we used in the past, was to set `deny_unknown_fields`,
/// which fails deserialization, and hence pageserver startup, if there is an unknown field.
/// The reason we don't do that anymore is that it complicates
/// usage of config fields for feature flagging, which we commonly do for
/// region-by-region rollouts.
/// The complications mainly arise because the `pageserver.toml` contents on a
/// prod server have a separate lifecycle from the pageserver binary.
/// For instance, `pageserver.toml` contents today are defined in the internal
/// infra repo, and thus introducing a new config field to pageserver and
/// rolling it out to prod servers are separate commits in separate repos
/// that can't be made or rolled back atomically.
/// Rollbacks in particular pose a risk with deny_unknown_fields because
/// the old pageserver binary may reject a new config field, resulting in
/// an outage unless the person doing the pageserver rollback remembers
/// to also revert the commit that added the config field in to the
/// `pageserver.toml` templates in the internal infra repo.
/// (A pre-deploy config check would eliminate this risk during rollbacks,
/// cf [here](https://github.com/neondatabase/cloud/issues/24349).)
/// In addition to this compatibility problem during emergency rollbacks,
/// deny_unknown_fields adds further complications when decomissioning a feature
/// flag: with deny_unknown_fields, we can't remove a flag from the [`ConfigToml`]
/// until all prod servers' `pageserver.toml` files have been updated to a version
/// that doesn't specify the flag. Otherwise new software would fail to start up.
/// This adds the requirement for an intermediate step where the new config field
/// is accepted but ignored, prolonging the decomissioning process by an entire
/// release cycle.
/// By contrast with unknown fields silently ignored, decomissioning a feature
/// flag is a one-step process: we can skip the intermediate step and straight
/// remove the field from the [`ConfigToml`]. We leave the field in the
/// `pageserver.toml` files on prod servers until we reach certainty that we
/// will not roll back to old software whose behavior was dependent on config.
/// Then we can remove the field from the templates in the internal infra repo.
/// This process is [documented internally](
/// https://docs.neon.build/storage/pageserver_configuration.html).
///
/// Note that above relaxed compatbility for the config format does NOT APPLY
/// TO THE STORAGE FORMAT. As general guidance, when introducing storage format
/// changes, ensure that the potential rollback target version will be compatible
/// with the new format. This must hold regardless of what flags are set in in the `pageserver.toml`:
/// any format version that exists in an environment must be compatible with the software that runs there.
/// Use a pageserver.toml flag only to gate whether software _writes_ the new format.
/// For more compatibility considerations, refer to [internal docs](
/// https://docs.neon.build/storage/compat.html?highlight=compat#format-versions--compatibility)
#[serde_as]
#[derive(Clone, Debug, serde::Deserialize, serde::Serialize)]
#[serde(default, deny_unknown_fields)]
#[serde(default)]
pub struct ConfigToml {
// types mapped 1:1 into the runtime PageServerConfig type
pub listen_pg_addr: String,
@@ -134,7 +179,6 @@ pub struct ConfigToml {
}
#[derive(Debug, Clone, PartialEq, Eq, serde::Serialize, serde::Deserialize)]
#[serde(deny_unknown_fields)]
pub struct DiskUsageEvictionTaskConfig {
pub max_usage_pct: utils::serde_percent::Percent,
pub min_avail_bytes: u64,
@@ -149,13 +193,11 @@ pub struct DiskUsageEvictionTaskConfig {
#[derive(Debug, Clone, PartialEq, Eq, serde::Serialize, serde::Deserialize)]
#[serde(tag = "mode", rename_all = "kebab-case")]
#[serde(deny_unknown_fields)]
pub enum PageServicePipeliningConfig {
Serial,
Pipelined(PageServicePipeliningConfigPipelined),
}
#[derive(Debug, Clone, PartialEq, Eq, serde::Serialize, serde::Deserialize)]
#[serde(deny_unknown_fields)]
pub struct PageServicePipeliningConfigPipelined {
/// Causes runtime errors if larger than max get_vectored batch size.
pub max_batch_size: NonZeroUsize,
@@ -171,7 +213,6 @@ pub enum PageServiceProtocolPipelinedExecutionStrategy {
#[derive(Debug, Clone, PartialEq, Eq, serde::Serialize, serde::Deserialize)]
#[serde(tag = "mode", rename_all = "kebab-case")]
#[serde(deny_unknown_fields)]
pub enum GetVectoredConcurrentIo {
/// The read path is fully sequential: layers are visited
/// one after the other and IOs are issued and waited upon
@@ -242,7 +283,7 @@ pub struct MaxVectoredReadBytes(pub NonZeroUsize);
/// Tenant-level configuration values, used for various purposes.
#[derive(Debug, Clone, PartialEq, Eq, serde::Serialize, serde::Deserialize)]
#[serde(deny_unknown_fields, default)]
#[serde(default)]
pub struct TenantConfigToml {
// Flush out an inmemory layer, if it's holding WAL older than this
// This puts a backstop on how much WAL needs to be re-digested if the
libs/pageserver_api/src/models.rs
+1 -1
View File
@@ -1105,7 +1105,7 @@ pub struct CompactionAlgorithmSettings {
}
#[derive(Debug, PartialEq, Eq, Clone, Deserialize, Serialize)]
#[serde(tag = "mode", rename_all = "kebab-case", deny_unknown_fields)]
#[serde(tag = "mode", rename_all = "kebab-case")]
pub enum L0FlushConfig {
#[serde(rename_all = "snake_case")]
Direct { max_concurrency: NonZeroUsize },
pageserver/src/config.rs
-79
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@@ -526,7 +526,6 @@ impl PageServerConf {
}
#[derive(serde::Deserialize, serde::Serialize)]
#[serde(deny_unknown_fields)]
pub struct PageserverIdentity {
pub id: NodeId,
}
@@ -598,82 +597,4 @@ mod tests {
PageServerConf::parse_and_validate(NodeId(0), config_toml, &workdir)
.expect("parse_and_validate");
}
/// If there's a typo in the pageserver config, we'd rather catch that typo
/// and fail pageserver startup than silently ignoring the typo, leaving whoever
/// made it in the believe that their config change is effective.
///
/// The default in serde is to allow unknown fields, so, we rely
/// on developer+review discipline to add `deny_unknown_fields` when adding
/// new structs to the config, and these tests here as a regression test.
///
/// The alternative to all of this would be to allow unknown fields in the config.
/// To catch them, we could have a config check tool or mgmt API endpoint that
/// compares the effective config with the TOML on disk and makes sure that
/// the on-disk TOML is a strict subset of the effective config.
mod unknown_fields_handling {
macro_rules! test {
($short_name:ident, $input:expr) => {
#[test]
fn $short_name() {
let input = $input;
let err = toml_edit::de::from_str::<pageserver_api::config::ConfigToml>(&input)
.expect_err("some_invalid_field is an invalid field");
dbg!(&err);
assert!(err.to_string().contains("some_invalid_field"));
}
};
}
use indoc::indoc;
test!(
toplevel,
indoc! {r#"
some_invalid_field = 23
"#}
);
test!(
toplevel_nested,
indoc! {r#"
[some_invalid_field]
foo = 23
"#}
);
test!(
disk_usage_based_eviction,
indoc! {r#"
[disk_usage_based_eviction]
some_invalid_field = 23
"#}
);
test!(
tenant_config,
indoc! {r#"
[tenant_config]
some_invalid_field = 23
"#}
);
test!(
l0_flush,
indoc! {r#"
[l0_flush]
mode = "direct"
some_invalid_field = 23
"#}
);
// TODO: fix this => https://github.com/neondatabase/neon/issues/8915
// test!(
// remote_storage_config,
// indoc! {r#"
// [remote_storage_config]
// local_path = "/nonexistent"
// some_invalid_field = 23
// "#}
// );
}
}