## Problem
Disk usage eviction isn't sensitive to layers of imported timelines.
## Summary of changes
Hook importing timelines up into eviction and add a test for it.
I don't think we need any special eviction logic for this. These layers
will all be visible and
their access time will be their creation time. Hence, we'll remove
covered layers first
and get to the imported layers if there's still disk pressure.
## Problem
Importing timelines can't currently be deleted. This is problematic
because:
1. Cplane cannot delete failed imports and we leave the timeline behind.
2. The flow does not support user driven cancellation of the import
## Summary of changes
On the pageserver: I've taken the path of least resistance, extended
`TimelineOrOffloaded`
with a new variant and added handling in the right places. I'm open to
thoughts here,
but I think it turned out better than I was envisioning.
On the storage controller: Again, fairly simple business: when a DELETE
timeline request is
received, we remove the import from the DB and stop any finalization
tasks/futures. In order
to stop finalizations, we track them in-memory. For each finalizing
import, we associate a gate
and a cancellation token.
Note that we delete the entry from the database before cancelling any
finalizations. This is such
that a concurrent request can't progress the import into finalize state
and race with the deletion.
This concern about deleting an import with on-going finalization is
theoretical in the near future.
We are only going to delete importing timelines after the storage
controller reports the failure to
cplane. Alas, the design works for user driven cancellation too.
Closes https://github.com/neondatabase/neon/issues/11897
The `test_storcon_create_delete_sk_down` test is still flaky. This test
addresses two possible causes for flakiness. both causes are related to
deletion racing with `pull_timeline` which hasn't finished yet.
* the first cause is timeline deletion racing with `pull_timeline`:
* the first deletion attempt doesn't contain the line because the
timeline doesn't exist yet
* the subsequent deletion attempts don't contain it either, only a note
that the timeline is already deleted.
* so this patch adds the note that the timeline is already deleted to
the regex
* the second cause is about tenant deletion racing with `pull_timeline`:
* there were no tenant specific tombstones so if a tenant was deleted,
we only added tombstones for the specific timelines being deleted, not
for the tenant itself.
* This patch changes this, so we now have tenant specific tombstones as
well as timeline specific ones, and creation of a timeline checks both.
* we also don't see any retries of the tenant deletion in the logs. once
it's done it's done. so extend the regex to contain the tenant deletion
message as well.
One could wonder why the regex and why not using the API to check
whether the timeline is just "gone". The issue with the API is that it
doesn't allow one to distinguish between "deleted" and "has never
existed", and latter case might race with `pull_timeline`. I.e. the
second case flakiness helped in the discovery of a real bug (no tenant
tombstones), so the more precise check was helpful.
Before, I could easily reproduce 2-9 occurences of flakiness when
running the test with an additional `range(128)` parameter (i.e. 218
times 4 times). With this patch, I ran it three times, not a single
failure.
Fixes#11838
## Problem
Previous attempt https://github.com/neondatabase/neon/pull/10548 caused
some issues in staging and we reverted it. This is a re-attempt to
address https://github.com/neondatabase/neon/issues/11063.
Currently we create image layers at latest record LSN. We would create
"future image layers" (i.e., image layers with LSN larger than disk
consistent LSN) that need special handling at startup. We also waste a
lot of read operations to reconstruct from L0 layers while we could have
compacted all of the L0 layers and operate on a flat level of historic
layers.
## Summary of changes
* Run repartition at L0-L1 boundary.
* Roll out with feature flags.
* Piggyback a change that downgrades "image layer creating below
gc_cutoff" to debug level.
---------
Signed-off-by: Alex Chi Z <chi@neon.tech>
Some tests still explicitly specify version 3 of the safekeeper
walproposer protocol. Remove the explicit opt in from the tests as v3 is
the default now since #11518.
We don't touch the places where a test exercises both v2 and v3. Those
we leave for #12021.
Part of https://github.com/neondatabase/neon/issues/10326
## Problem
Test coverage of timeline imports is lacking.
## Summary of changes
This PR adds a chaos import test. It runs an import while injecting
various chaos events
in the environment. All the commits that follow the test fix various
issues that were surfaced by it.
Closes https://github.com/neondatabase/neon/issues/10191
Support timeline creations on the storage controller to opt out from
their creation on the safekeepers, introducing the read-only timelines
concept. Read only timelines:
* will never receive WAL of their own, so it's fine to not create them
on the safekeepers
* the property is non-transitive. children of read-only timelines aren't
neccessarily read-only themselves.
This feature can be used for snapshots, to prevent the safekeepers from
being overloaded by empty timelines that won't ever get written to. In
the current world, this is not a problem, because timelines are created
implicitly by the compute connecting to a safekeeper that doesn't have
the timeline yet. In the future however, where the storage controller
creates timelines eagerly, we should watch out for that.
We represent read-only timelines in the storage controller database so
that we ensure that they never touch the safekeepers at all. Especially
we don't want them to cause a mess during the importing process of the
timelines from the cplane to the storcon database.
In a hypothetical future where we have a feature to detach timelines
from safekeepers, we'll either need to find a way to distinguish the
two, or if not, asking safekeepers to list the (empty) timeline prefix
and delete everything from it isn't a big issue either.
This patch will unconditionally hit the new safekeeper timeline creation
path for read-only timelines, without them needing the
`--timelines-onto-safekeepers` flag enabled. This is done because it's
lower risk (no safekeepers or computes involved at all) and gives us
some initial way to verify at least some parts of that code in prod.
https://github.com/neondatabase/cloud/issues/29435https://github.com/neondatabase/neon/issues/11670
## Problem
We want to expose the page service over gRPC, for use with the
communicator.
Requires #11995.
Touches #11728.
## Summary of changes
This patch wires up a gRPC server in the Pageserver, using Tonic. It
does not yet implement the actual page service.
* Adds `listen_grpc_addr` and `grpc_auth_type` config options (disabled
by default).
* Enables gRPC by default with `neon_local`.
* Stub implementation of `page_api.PageService`, returning unimplemented
errors.
* gRPC reflection service for use with e.g. `grpcurl`.
Subsequent PRs will implement the actual page service, including
authentication and observability.
Notably, TLS support is not yet implemented. Certificate reloading
requires us to reimplement the entire Tonic gRPC server.
## Problem
- Benchmark periodic pagebench had inconsistent benchmarking results
even when run with the same commit hash.
Hypothesis is this was due to running on dedicated but virtualized EC
instance with varying CPU frequency.
- the dedicated instance type used for the benchmark is quite "old" and
we increasingly get `An error occurred (InsufficientInstanceCapacity)
when calling the StartInstances operation (reached max retries: 2):
Insufficient capacity.`
- periodic pagebench uses a snapshot of pageserver timelines to have the
same layer structure in each run and get consistent performance.
Re-creating the snapshot was a painful manual process (see
https://github.com/neondatabase/cloud/issues/27051 and
https://github.com/neondatabase/cloud/issues/27653)
## Summary of changes
- Run the periodic pagebench on a custom hetzner GitHub runner with
large nvme disk and governor set to defined perf profile
- provide a manual dispatch option for the workflow that allows to
create a new snapshot
- keep the manual dispatch option to specify a commit hash useful for
bi-secting regressions
- always use the newest created snapshot (S3 bucket uses date suffix in
S3 key, example
`s3://neon-github-public-dev/performance/pagebench/shared-snapshots-2025-05-17/`
- `--ignore`
`test_runner/performance/pageserver/pagebench/test_pageserver_max_throughput_getpage_at_latest_lsn.py`
in regular benchmarks run for each commit
- improve perf copying snapshot by using `cp` subprocess instead of
traversing tree in python
## Example runs with code in this PR:
- run which creates new snapshot
https://github.com/neondatabase/neon/actions/runs/15083408849/job/42402986376#step:19:55
- run which uses latest snapshot
-
https://github.com/neondatabase/neon/actions/runs/15084907676/job/42406240745#step:11:65
## Problem
Basebackup cache is on the hot path of compute startup and is generated
on every request (may be slow).
- Issue: https://github.com/neondatabase/cloud/issues/29353
## Summary of changes
- Add `BasebackupCache` which stores basebackups on local disk.
- Basebackup prepare requests are triggered by
`XLOG_CHECKPOINT_SHUTDOWN` records in the log.
- Limit the size of the cache by number of entries.
- Add `basebackup_cache_enabled` feature flag to TenantConfig.
- Write tests for the cache
## Not implemented yet
- Limit the size of the cache by total size in bytes
---------
Co-authored-by: Aleksandr Sarantsev <aleksandr@neon.tech>
## Problem
For billing, we'd like per-branch consumption metrics.
Requires https://github.com/neondatabase/neon/pull/11984.
Resolves https://github.com/neondatabase/cloud/issues/28155.
## Summary of changes
This patch adds two new consumption metrics:
* `written_size_since_parent`: `written_size - ancestor_lsn`
* `pitr_history_size_since_parent`: `written_size - max(pitr_cutoff,
ancestor_lsn)`
Note that `pitr_history_size_since_parent` will not be emitted until the
PITR cutoff has been computed, and may or may not increase ~immediately
when a user increases their PITR window (depending on how much history
we have available and whether the tenant is restarted/migrated).
## Problem
See
Discussion:
https://neondb.slack.com/archives/C033RQ5SPDH/p1746645666075799
Issue: https://github.com/neondatabase/cloud/issues/28609
Relation size cache is not correctly updated at PS in case of replicas.
## Summary of changes
1. Have two caches for relation size in timeline:
`rel_size_primary_cache` and `rel_size_replica_cache`.
2. `rel_size_primary_cache` is actually what we have now. The only
difference is that it is not updated in `get_rel_size`, only by WAL
ingestion
3. `rel_size_replica_cache` has limited size (LruCache) and it's key is
`(Lsn,RelTag)` . It is updated in `get_rel_size`. Only strict LSN
matches are accepted as cache hit.
---------
Co-authored-by: Konstantin Knizhnik <knizhnik@neon.tech>
## Problem
In the escaping path we were checking that `${tag}$` or `${outer_tag}$`
are present in the string, but that's not enough, as original string
surrounded by `$` can also form a 'tag', like `$x$xx$x$`, which is fine
on it's own, but cannot be used in the string escaped with `$xx$`.
## Summary of changes
Remove `$` from the checks, just check if `{tag}` or `{outer_tag}` are
present. Add more test cases and change the catalog test to stress the
`drop_subscriptions_before_start: true` path as well.
Fixes https://github.com/neondatabase/cloud/issues/29198
## Problem
Currently the `logger` library throws annoying deprecation warnings:
```python
DeprecationWarning: The 'warn' method is deprecated, use 'warning' instead
```
## Summary of changes
This small PR resolves the annoying deprecation warnings by migrating to
`.warning` as suggested.
Signed-off-by: Emmanuel Ferdman <emmanuelferdman@gmail.com>
This PR commits the benchmarks I ran to qualify concurrent IO before we
released it.
Changes:
- Add `l0stack` fixture; a reusable abstraction for creating a stack of
L0 deltas
each of which has 1 Value::Delta per page.
- Such a stack of L0 deltas is a good and understandable demo for
concurrent IO
because to reconstruct any page, $layer_stack_height` Values need to be
read.
Before concurrent IO, the reads were sequential.
With concurrent IO, they are executed concurrently.
- So, switch `test_latency` to use the l0stack.
- Teach `pagebench`, which is used by `test_latency`, to limit itself to
the blocks of the relation created by the l0stack abstraction.
- Additional parametrization of `test_latency` over dimensions
`ps_io_concurrency,l0_stack_height,queue_depth`
- Use better names for the tests to reflect what they do, leave
interpretation of the (now quite high-dimensional) results to the reader
- `test_{throughput => postgres_seqscan}`
- `test_{latency => random_reads}`
- Cut down on permutations to those we use in production. Runtime is
about 2min.
Refs
- concurrent IO epic https://github.com/neondatabase/neon/issues/9378
- batching task: fixes https://github.com/neondatabase/neon/issues/9837
---------
Co-authored-by: Peter Bendel <peterbendel@neon.tech>
## Problem
Timeline imports do not have progress checkpointing. Any time that the
tenant is shut-down, all progress is lost
and the import restarts from the beginning when the tenant is
re-attached.
## Summary of changes
This PR adds progress checkpointing.
### Preliminaries
The **unit of work** is a `ChunkProcessingJob`. Each
`ChunkProcessingJob` deals with the import for a set of key ranges. The
job split is done by using an estimation of how many pages each job will
produce.
The planning stage must be **pure**: given a fixed set of contents in
the import bucket, it will always yield the same plan. This property is
enforced by checking that the hash of the plan is identical when
resuming from a checkpoint.
The storage controller tracks the progress of each shard in the import
in the database in the form of the **latest
job** that has has completed.
### Flow
This is the high level flow for the happy path:
1. On the first run of the import task, the import task queries storcon
for the progress and sees that none is recorded.
2. Execute the preparatory stage of the import
3. Import jobs start running concurrently in a `FuturesOrdered`. Every
time the checkpointing threshold of jobs has been reached, notify the
storage controller.
4. Tenant is detached and re-attached
5. Import task starts up again and gets the latest progress checkpoint
from the storage controller in the form of a job index.
6. The plan is computed again and we check that the hash matches with
the original plan.
7. Jobs are spawned from where the previous import task left off. Note
that we will not report progress after the completion of each job, so
some jobs might run twice.
Closes https://github.com/neondatabase/neon/issues/11568
Closes https://github.com/neondatabase/neon/issues/11664
## Problem
Lifetime of imported timelines (and implicitly the import background
task) has some shortcomings:
1. Timeline activation upon import completion is tricky. Previously, a
timeline that finished importing
after a tenant detach would not get activated and there's concerns about
the safety of activating
concurrently with shut-down.
2. Import jobs can prevent tenant shut down since they hold the tenant
gate
## Summary of Changes
Track the import tasks in memory and abort them explicitly on tenant
shutdown.
Integrate more closely with the storage controller:
1. When an import task has finished all of its jobs, it notifies the
storage controller, but **does not** mark the import as done in the
index_part. When all shards have finished importing, the storage
controller will call the `/activate_post_import` idempotent endpoint for
all of them. The handler, marks the import complete in index part,
resets the tenant if required and checks if the timeline is active yet.
2. Not directly related, but the import job now gets the starting state
from the storage controller instead of the import bucket. This paves the
way for progress checkpointing.
Related: https://github.com/neondatabase/neon/issues/11568
## Problem
We realised that pg-sni-router doesn't need to be separate from proxy.
just a separate port.
## Summary of changes
Add pg-sni-router config to proxy and expose the service.
This PR adds a runtime validation mode to check adherence to alignment
and size-multiple requirements at the VirtualFile level.
This can help prevent alignment bugs from slipping into production
because test systems may have more lax requirements than production.
(This is not the case today, but it could change in the future).
It also allows catching O_DIRECT bugs on systems that don't have
O_DIRECT (macOS).
Consequently, we can now accept
`virtual_file_io_mode={direct,direct-rw}` on macOS now.
This has the side benefit of removing some annoying conditional
compilation around `IoMode`.
A third benefit is that it helped weed out size-multiple requirement
violation bugs in how the VirtualFile unit tests exercise read and write
APIs.
I seized the opportunity to trim these tests down to what actually
matters, i.e., exercising of the `OpenFiles` file descriptor cache.
Lastly, this PR flips the binary-built-in default to `DirectRw` so that
when running Python regress tests and benchmarks without specifying
`PAGESERVER_VIRTUAL_FILE_IO_MODE`, one gets the production behavior.
Refs
- fixes https://github.com/neondatabase/neon/issues/11676
PR
- github.com/neondatabase/neon/pull/11864
committed yesterday rendered the `PAGESERVER_VIRTUAL_FILE_IO_MODE`
env-var-based parametrization ineffective.
As a consequence, the tests and benchmarks in `test_runner/` were using
the binary built-in-default, i.e., `buffered`.
## Problem
SK timeline creations were skipped for imported timelines since we
didn't know the correct start LSN
of the timeline at that point.
## Summary of changes
Created imported timelines on the SK as part of the import finalize
step.
We use the last record LSN of shard 0 as the start LSN for the
safekeeper timeline.
Closes https://github.com/neondatabase/neon/issues/11569
## Problem
Read replicas cannot grant permissions for roles for Neon RLS. Usually
the permission is already granted, so we can optimistically check. See
INC-509
## Summary of changes
Perform a permission lookup prior to actually executing any grants.
## Problem
We want to see how many users of the legacy serverless driver are still
using the old URL for SQL-over-HTTP traffic.
## Summary of changes
Adds a protocol field to the connections_by_sni metric. Ensures it's
incremented for sql-over-http.
Second PR with fixes extracted from #11712, relating to
`--timelines-onto-safekeepers`. Does the following:
* Moves safekeeper registration to `neon_local` instead of the test
fixtures
* Pass safekeeper JWT token if `--timelines-onto-safekeepers` is enabled
* Allow some warnings related to offline safekeepers (similarly to how
we allow them for offline pageservers)
* Enable generations on the compute's config if
`--timelines-onto-safekeepers` is enabled
* fix parallel `pull_timeline` race condition (the one that #11786 put
for later)
Fixes#11424
Part of #11670
## Problem
Compute may flush WAL on page boundaries, leaving some records partially
flushed for a long time.
It leads to `wait_for_last_flush_lsn` stuck waiting for this partial
LSN.
- Closes: https://github.com/neondatabase/cloud/issues/27876
## Summary of changes
- Flush WAL via CHECKPOINT after requesting current_wal_lsn to make sure
that the record we point to is flushed in full
- Use proper endpoint in
`test_timeline_detach_with_aux_files_with_detach_v1`
Corrects the postgres extension s3 gateway address to
be not just a domain name but a full base URL.
To make the code more readable, the option is renamed
to "remote_ext_base_url", while keeping the old name
also accessible by providing a clap argument alias.
Also provides a very simple and, perhaps, even redundant
unit test to confirm the logic behind parsing of the
corresponding CLI argument.
## Problem
As it is clearly stated in
https://github.com/neondatabase/cloud/issues/26005, using of the short
version of the domain name might work for now, but in the future, we
should get rid of using the `default` namespace and this is where it
will, most likely, break down.
## Summary of changes
The changes adjust the domain name of the extension s3 gateway to use
the proper base url format instead of the just domain name assuming the
"default" namespace and add a new CLI argument name for to reflect the
change and the expectance.
## Problem
Users can override some configuration parameters on the DB level with
`ALTER DATABASE ... SET ...`. Some of these overrides, like `role` or
`default_transaction_read_only`, affect `compute_ctl`'s ability to
configure the DB schema properly.
## Summary of changes
Enforce `role=cloud_admin`, `statement_timeout=0`, and move
`default_transaction_read_only=off` override from control plane [1] to
`compute_ctl`. Also, enforce `search_path=public` just in case, although
we do not call any functions in user databases.
[1]:
133dd8c4db/goapp/controlplane/internal/pkg/compute/provisioner/provisioner_common.go (L70)
Fixes https://github.com/neondatabase/cloud/issues/28532
According to RFC 7519, `aud` is generally an array of StringOrURI, but
in special cases may be a single StringOrURI value. To accomodate future
control plane work where a single token may work for multiple services,
make the claim a vector.
Link: https://www.rfc-editor.org/rfc/rfc7519#section-4.1.3
Signed-off-by: Tristan Partin <tristan@neon.tech>
Add `/lfc/(prewarm|offload)` routes to `compute_ctl` which interact with
endpoint storage.
Add `prewarm_lfc_on_startup` spec option which, if enabled, downloads
LFC prewarm data on compute startup.
Resolves: https://github.com/neondatabase/cloud/issues/26343
Currently we only have an admin scope which allows a user to bypass the
compute_id check. When the admin scope is provided, validate the
audience of the JWT to be "compute".
Closes: https://github.com/neondatabase/cloud/issues/27614
Signed-off-by: Tristan Partin <tristan@neon.tech>
## Problem
When aborting a split, the code accidentally removes all other tenant
shards from the in-memory map that have the same shard count as the
aborted split, causing "tenant not found" errors. It will recover on a
storcon restart, when it loads the persisted state. This issue has been
present for at least a year.
Resolves https://github.com/neondatabase/cloud/issues/28589.
## Summary of changes
Only remove shards belonging to the relevant tenant when aborting a
split.
Also adds a regression test.
## Problem
- some projects are created during GitHub workflows but not by action
project_create but by python test scripts.
If the python test fails the project is not deleted
## Summary of changes
- make sure we cleanup those python created projects a few days after
they are no longer used, too
## Problem
Part of https://github.com/neondatabase/neon/issues/11762
## Summary of changes
While #11762 needs some work to refactor the error propagating thing, we
can do a hacky fix for the gc-compaction tests to allow flush error
during shutdown. It does not affect correctness.
Signed-off-by: Alex Chi Z <chi@neon.tech>
## Problem
Those tests are timing out more frequently after
https://github.com/neondatabase/neon/pull/11585
## Summary of changes
Increase timeout for `test_pageserver_gc_compaction_smoke`
Increase rollback wait timeout for `test_tx_abort_with_many_relations`
Signed-off-by: Alex Chi Z <chi@neon.tech>
## Problem
part of https://github.com/neondatabase/neon/issues/9516
One thing I realized in the past few months is that "no-way-back" things
like this are scary to roll out without a fine-grained rollout infra.
The plan was to flip the flag in the repo and roll it out soon, but I
don't think rolling out would happen in the near future. So I'd rather
revert the flag to avoid creating a discrepancy between staging and the
regress tests.
## Summary of changes
Not using rel_size_v2 by default in unit tests; we still have a few
tests to explicitly test the new format so we still get some test
coverages.
---------
Signed-off-by: Alex Chi Z <chi@neon.tech>
This is a rebase of PR #10739 by @henryliu2014 on the current main
branch.
## Problem
pageserver: remove resident size from billing metrics
Fixes#10388
## Summary of changes
The following changes have been made to remove resident size from
billing metrics:
* removed the metric "resident_size" and related codes in
consumption_metrics/metrics.rs
* removed the item of the description of metric "resident_size" in
consumption_metrics.md
* refactored the metric "resident_size" related test case
Requested by: John Spray (john@neon.tech)
---------
Co-authored-by: liuheqing <hq.liu@qq.com>
Co-authored-by: Devin AI <158243242+devin-ai-integration[bot]@users.noreply.github.com>
Co-authored-by: John Spray <john@neon.tech>
In order for the test to work when sanitizers are enabled, we would need
to compile the dummy Postgres extension with the same sanitizer flags
that we compile Postgres and the neon extension with. Doing this work
would be a little more than trivial, so skipping is the best option, at
least for now.
Signed-off-by: Tristan Partin <tristan@neon.tech>
## Problem
We had retained the ability to run in a generation-less mode to support
test_generations_upgrade, which was replaced with a cleaner backward
compat test in https://github.com/neondatabase/neon/pull/10701
## Summary of changes
- Remove all the special cases for "if no generation" or "if no control
plane api"
- Make control_plane_api config mandatory
---------
Co-authored-by: Arpad Müller <arpad-m@users.noreply.github.com>
## Problem
Broker supports only HTTP, no HTTPS
- Closes: https://github.com/neondatabase/cloud/issues/27492
## Summary of changes
- Add `listen_https_addr`, `ssl_key_file`, `ssl_cert_file`,
`ssl_cert_reload_period` arguments to storage broker
- Make `listen_addr` argument optional
- Listen https in storage broker
- Support https for storage broker request in neon_local
- Add `use_https_storage_broker_api` option to NeonEnvBuilder
The current test was just SQL files only, but we also want to test a
remote extension which includes a loadable library. With both extensions
we should cover a larger portion of compute_ctl's remote extension code
paths.
Fixes: https://github.com/neondatabase/neon/issues/11146
Signed-off-by: Tristan Partin <tristan@neon.tech>
## Problem
In https://github.com/neondatabase/neon/pull/11345 coordination of
imports moved to the storage controller.
It involves notifying cplane when the import has been completed by
calling an idempotent endpoint.
If the storage controller shuts down in the middle of finalizing an
import, it would never be retried.
## Summary of changes
Reconcile imports at start-up by fetching the complete imports from the
database and spawning a background
task which notifies cplane.
Closes: https://github.com/neondatabase/neon/issues/11570
## Problem
We saw the following scenario in staging:
1. Pod A starts up. Becomes leader and steps down the previous pod
cleanly.
2. Pod B starts up (deployment).
3. Step down request from pod B to pod A times out. Pod A did not manage
to stop its reconciliations within 10 seconds and exited with return
code 1
([code](7ba8519b43/storage_controller/src/service.rs (L8686-L8702))).
4. Pod B marks itself as the leader and finishes start-up
5. k8s restarts pod A
6. k8s marks pod B as ready
7. pod A sends step down request to pod A - this succeeds => pod A is
now the leader
8. k8s kills pod A because it thinks pod B is healthy and pod A is part
of the old replica set
We end up in a situation where the only pod we have (B) is stepped down
and attempts to forward requests to a leader that doesn't exist. k8s
can't detect that pod B is in a bad state since the /status endpoint
simply returns 200 hundred if the pod is running.
## Summary of changes
This PR includes a number of robustness improvements to the leadership
protocol:
* use a single step down task per controller
* add a new endpoint to be used as k8s liveness probe and check
leadership status there
* handle restarts explicitly (i.e. don't step yourself down)
* increase the step down retry count
* don't kill the process on long step down since k8s will just restart
it
